Fluvial Redistribution of Chernobyl Fallout: Reservoir Evidence in the Severn Basin

Sediments in the Chelmarsh pump-storage reservoir have provided a valuable record of the ¹³⁷Cs levels associated with suspended particulates transported by the River Severn since 1965. The presence of Chernobyl-derived ¹³⁷Cs and ¹³⁴Cs within the sedimentary record of the site, despite the absence of any direct fallout on the local area, confirmed that radiocaesium from the Ukrainian reactor accident has been mobilized from the upper reaches of the Severn basin where atmospheric deposition was relatively high. The incorporation of Chernobyl radiocaesium within these sediments can be used to date the 1986 fallout episode, and the established geochronology indicated variable rates of post-1986 sediment accumulation. As radiocaesium is strongly bound to fluvial particulates, this mechanism of redistribution has not adversely affected the quality of the drinking-water source at the site which was studied.     

Risk Assessment for a Proposed Groundwater Abstraction Scheme in Strathmore, North-East Scotland: a Modelling Approach

The Lower Old Red Sandstones in northern Strathmore have favourable hydrogeological conditions for ground-water development. A scheme was proposed to abstract water in the north Esk catchment in order to augment water supplies to local villages, and a production borehole was drilled into the Edzell Sandstones to give a design yield of 2420 m³/d. However, this scheme has been abandoned because of concern that the abstraction would significantly reduce the flow in a nearby stream which is an important salmonid fishery.
This study demonstrates the potential value of using a stream-aquifer numerical model in an environmental risk assessment for the proposed scheme.     

Tritium Levels in Leachates and Condensates from Domestic Wastes in Landfill Sites

An extensive review study of leachate composition, from landfills which have received mainly domestic wastes in the UK, has been carried out by Aspinwall & Company on behalf of the Department of the Environment. This work has provided detailed information on concentrations of a wide range of determinands. One set of analyses which has produced particularly interesting results comprises the determination of tritium. Tritium is a natural isotope of hydrogen (³H), with a half-life of 12.43 years, which decays radioactively to form stable ³He atoms, releasing beta particles. Although tritium concentrations can be measured accurately as tritium units (TU), these represent extremely low levels of activity, and concentrations of tritium well in excess of 100 000 TU would be needed before acceptable levels of radio-activity in drinking water were exceeded.
Background levels of tritium in UK rainfall rarely now exceed 50 TU although, in the 1960s, values of up to 3000 TU in rainfall were associated with atmospheric testing of atomic weapons. It was somewhat surprising, therefore, to discover that relatively high concentrations of tritium (>10 000 TU) were widespread in leachates from landfills which had received primarily domestic wastes. This paper presents results from samples taken at 30 representative UK sites, and discusses potential sources of tritium.     

Chlorination and Drinking Water Quality - an Operational Overview

A vailable national guidelines for disinfection practice, and for the examination of bacteriological quality, are reviewed, together with the legislative requirements of the EC 'Drinking Water'Directive. Problems of impracticability, vagueness, and ambiguity are identified.
Experience of the maintenance of bacteriological quality in large, lowland, surface water and ground-water supply areas is given with reference to the behaviour of disinfectant residuals, trihalomethanes, nitrite, and aesthetic parameters. The way forward in terms of the management of distribution systems and water treatment is discussed.     

A Simple Aid for Designing Sewers

A method for constructing design charts for the rapid selection of sewer diameter and gradient is described. A variety of design criteria for sewer capacity and minimum gradient can be incorporated in the chart, which may be adapted for different ranges of pipe diameter and material. The use of the chart should ensure that the most economical combination of pipe diameter and gradient can be chosen without the need for calculation.     

POLYMERS IN ALUM SLUDGE DEWATERING: DEVELOPMENTS AND CONTROL

The paper (a) discusses the use of polymers for conditioning alum sludge derived from the coagulation of low turbidity coloured waters, and (b) reviews the factors which control the optimum dosage vis a vis individual test methods such as specific resistance to filtration and capillary suction time. It was demonstrated that good estimates of the solids feed could be obtained via the suspended-solids concentration in the flocculators. An algorithm based on water-quality parameters was recommended for planning purposes. Difficulties arising from variations in the solids delivery to the thickeners were shown to influence the separation efficiency. The paper also includes a survey of polymer routeing within a water-treatment plant in which there was multiple polymer use and extensive recycling; this identified a number of quality-control issues and demonstrated the value of polymer measurement.     

The Thames Water Ring Main: The Future

Commissioning of the Thames Water ring main Phase 2 tunnels in the spring of 1994 signalled an important milestone for major investment on London's watertreatment and trunk distribution systems. This included not only the ring main itself, but also the progressive installation of advanced water treatment processes in the water-treatment works supplying the city, due for completion at the end of 1998.
This paper reviews the benefits of the ring main and looks at future developments, focused largely in local distribution rehabilitation and leakage control. The objectives and benefits of future possible extensions of the ring main are discussed, and a configuration is put forward as potential for development in the long term.     

The Design, Construction and Performance Assessment of a Storm King Storm-Sewage Overflow

A new storm-sewage overflow was commissioned in the spring of 1989 at Lochgelly, Fife, incorporating two proprietary Storm King overflow devices. A programme of monitoring their performance was carried out throughout 1989 to determine whether the units behaved satisfactorily and whether the discharge was equivalent to that passing a 10-mm screen.
The twin Storm King units each have a diameter of 7.2 m with a continuation flow of 110 1/s and a peak design inflow of 2530 1/s. The paper describes their design and construction, involving difficult access and site problems. Results are quoted from the sampling programme, which included flow measurement, automatic bottle sampling, and detailed visual evidence.     

Hydrological Data for Wetland Management

Hydrology is the prime control in wetland ecosystems, but little formal hydrological data are gathered in wetlands by hydrometric authorities. Normally, most of the hydrological data for wetlands can be obtained from informal sources, non-hydrological organizations, the local population and archival information - especially photographs. Some short-term field monitoring can be useful in augmenting the large hydrological data sets which can be gathered - even when initial enquiries yield minimum information. A case study from the North Kent Marshes is used to illustrate this fact.