Mechanisms of Groundwater Pollution by Pesticides

An increasing number of pesticide compounds are being detected in groundwater supplies worldwide. There has, nevertheless, been little research into the mechanisms by which such pollution occurs and the routes via which pesticides move from the land surface into aquifers. In view of the potential time-lag in the response of groundwater systems to pollution inputs, such knowledge is essential if the current situation is to be appraised adequately and if any necessary controls on pesticide use are to be introduced.
From basic data on the physicochemical properties of pesticide compounds and on groundwater flow and pollutant transport in the principal British aquifers, some useful observations can be made about the relative significance of different mechanisms of potential groundwater pollution. These mechanisms and their implications for field research on pesticide pollution of groundwater are discussed. This problem is compared and contrasted to that of nitrate pollution from agricultural land-use practices.     

Trash Screens on Culverts in Urban Areas

T his PAPER DEALS with the performance of trash screens on culverts on urban watercourses. An assessment of the scope of problems associated with screens has been obtained from a survey of land drainage authorities in urban areas in England and Wales. The findings have been analysed and this has resulted in the development of four basic design criteria for screens. A detailed survey of the performance of some 17 sites in the river Ravensbourne catchment of the Thames Water Authority was undertaken over a number of years allowing relationships to be identified between debris amounts and types of upstream catchment area, screen/culvert area ratios, and priority of location.
The paper describes considerations to be taken when providing a screen and advocates an individual design for each location rather than installing a standard arrangement. The lack of practical information in the UK, and the high level of problems experienced overall underlines the need for proper consideration to be given to this subject. Current research work is being undertaken to obtain preferred efficient screen configurations, but it is concluded that this should complement rather than replace the need for good trash screen design.     

The Impact of the EC Urban Waste Water Treatment Directive

During the last two years significant policy and legislative developments have taken place in the UK and in the EC in respect of sewage treatment and disposal and the dumping of sewage sludge at sea. Details of the UK Government's sewage-treatment initiative and its decision to stop the dumping of sewage sludge at sea by 1998 are described. An outline is given of the provisions of the EC urban waste water treatment Directive, in particular those provisions concerned with sewage treatment, trade effluent discharges from prescribed industrial sectors, and the termination of dumping of sewage sludge at sea. The implications of these developments for Scottish sewerage authorities are summarized and provisional estimated costs of meeting these new obligations are given. The opportunities available to contractors and equipment manufacturers are highlighted.     

Recent Developments in Application of 'Bursts and Background Estimates'Concepts for Leakage Management

ABSTRACT During the UK 'national leakage control initiative', which was carried out in 1991–94, Welsh Water formulated a conceptual model of leakage management which was intended for international application.
This paper explains how the concepts of 'bursts and background estimates'(BABE) have been calibrated and extended to cover financial/economic analysis and pressure management, using specialist software for practical application and following the methodologies in the recent water industry 'Managing Leakage'reports. Examples of applications of BABE software and concepts, in the UK and internationally, are also described.     

Milestones in the Development of the Activated-Sludge Process Over the Past Eighty Years (Abridged)

The biological filter was introduced during the latter part of the last century but, in 1913, a radical new process was developed which resulted in a four-fold reduction in the size of sewage-treatment plants. This new method was called the 'activated-sludge process', and whilst biological filters are still in use - especially for small works - activated sludge is now the dominant secondary treatment process and is the 'engine'around which modern treatment systems are constructed.
This paper (a) reviews the milestones in the evolution of the activated-sludge process from 1913 to 1954, centering on reliable removal of BOD and suspended solids, (b) highlights the improvements in design capabilities (1955-74), with the emphasis on the attainment of consistent nitrification, and (c) discusses the removal of nitrogen and phosphorus (1975-97), with brief reference to computer modelling and the control of sludge properties.     

Paying for Water: Policy Options and their Practical Implications

Paying for water supply, wastewater and surface water sewerage and treatment, and river basin management, is considered against the four strategic options of using taxation, charges to users, accepting environmental damage, and charitable funding. The different social consequences of each are addressed. A fundamental appraisal of issues of cost analysis is provided, and often overlooked factors are identified. The merits of (a) alternative tariff forms including rising and falling blocks, (b) seasonal and time-of-day tariffs, and (c) cover/fixed charge approaches are analysed, together with the often more cost-effective use of tariffs without meters for households. The important role of the engineering elasticity of demand is set alongside the more often discussed concept of economic elasticity.