Contamination of the Chalk Aquifer by Chlorinated Solvents: A Case Study of the Luton and Dunstable Area

A detailed investigation of contamination by chlorinated solvents of the Chalk Aquifer underlying the towns of Luton and Dunstable was undertaken to assess the extent, causes and mechanisms of pollution. The research programme incorporated land-use surveys, regional groundwater surveys, monitoring of groundwater abstraction points and aquifer profiling by means of the drilling of observation boreholes, the analysis of the recovered core material and the depth sampling of these and other boreholes.
Low-level solvent contamination of the Chalk Aquifer was found to be widespread with 'hotspots'of higher concentrations. At the drilling sites, both the saturated and unsaturated zones were contaminated with solvents, although free product was not observed. The presence of an additional contaminant, oil, at some sites was noted to influence the distribution of solvents within the aquifer.
Clean-up of the aquifer is not a practical option, and treatment of the groundwater at the abstraction points has been adopted.     

Some Hydrogeological Peculiar to Various Types of Problems Small Islands

There are many problems associated with the investigation of small island hydrogeology, including (i) the availability of data and the distribution of both spatial and temporal data sets, (ii) the dynamics of the groundwater to sea-water interface and the shape of the so-called groundwater lens, and (iii) the difficulties of evaluating recharge to groundwater and of calculating the volume of groundwater discharge to the sea. These issues are compounded by (a) the ratio of coast to area in small islands, (b) the problems of extreme topography, and (c) the identification of baseflow to rivers and streams. A simple classification of island types assists in evaluating hydro-geological regimes, and the importance of groundwater in an island context cannot be over-emphasised.     

Measurements of Head Variations within Observation Boreholes and their Implications for Groundwater Monitoring

As part of several groundwater investigations of the Permo-Triassic Sandstone aquifers in north west England, a detailed measurement of piezometric heads and groundwater flow within observation boreholes was made which showed that vertical differences of groundwater heads persist within aquifers. A number of case histories of these studies are presented, which are used to consider the impact of head variations on typical groundwater level and groundwater quality measurements taken in observation boreholes, with a view to recommending design criteria for observation boreholes and groundwater monitoring programmes.     

Landfill Lining for Leachate Containment

There is an increasing need for engineered liners to prevent the escape of leachate and to control the migration of landfill gas. This has been influenced by new European and UK legislation and codes of practice.
General principles of site design are explained, followed by a review of the advantages and disadvantages of different liner systems, including mineral liners (natural clay, mudrocks and soil/bentonite admixtures), geomembranes and composite liners.
The need for conservative factors of safety in site design and high standards of quality control, involving full-time supervision and independent certification of the installation works, are considered essential to ensure the effectiveness of the barrier.
There is no one ideal liner material. Composite mineral/geomembrane liners provide the highest degree of security against leakage and, as such, should be considered as 'the norm'rather than for use only in particularly high-risk situations.     

Impacts of Sewers on Groundwater Quality

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.     

Controlling Diffuse Pollution of Groundwater from Agriculture and Industry

The greatest threat of contamination to groundwater resources is posed by pollutants from diffuse sources, yet legislation in the UK has until recently been focused on point sources. The problem of widespread pollution from industrial sources is described and compared with that from agriculture. The legislative controls available under the Water Resources Act 1991 are outlined, and the approach adopted by the National Rivers Authority in its Groundwater Protection Policy is discussed with respect to the concept of groundwater vulnerability.     

Groundwater Rebound in the Leicestershire Coalfield

The Leicestershire coalfield has been mined for at least eight hundred years, the last deep mine closing in 1991. The earliest shallow mines on the exposed coalfield are not recorded on plan, but were later connected to the deeper workings in many seams. In order to protect the last deep mines, pumping was maintained from the abandoned mines to the north.
Water-table rebound was observed prior to closure, and is now affecting the surface. Increased emissions of poor-quality water into low-discharge surface water-courses are predicted. Renewed subsidence has implications for roads, services and property. Rising water levels will affect old opencast excavations and waste disposal sites.
Fieldwork and abandoned mine plan inspections have demonstrated renewed subsidence and evidence of increased emissions in those low-lying areas of the exposed coalfield which are believed to be most at risk.     

A NEW CONCEPTUAL GROUNDWATER-FLOW SYSTEM FOR THE CENTRAL SOUTH DOWNS AQUIFER

The central part of the South Downs Chalk aquifer is intensely used for public water supply. Although the aquifer has a long history of careful development and management, the outline conceptual groundwater-flow vision has not been formally investigated for many years. A major programme of work has now been completed which (a) provides a new insight into the hydraulic workings of the aquifer, and (b) highlights a number of hitherto poorly understood concepts controlling groundwater movement in the Chalk. These include the key role of geological structure and the occurrence of hard bands and karst-type groundwater flow as major controls over preferred flow-paths. The new conceptualisation concludes that the main discharge area for the aquifer is laterally to the north-south rivers and not directly southwards to the sea.     

Groundwater Resources: Balancing Perspectives on Key Issues Affecting Supply and Demand

Sustainable groundwater management requires (a) maximizing the use of aquifer storage to reduce water-supply costs while limiting environmental impacts, and (b) maximizing groundwater protection to reduce water-supply treatment needs while not unduly restricting land-use activities. These key issues are evaluated from the experience of a recent and comprehensive national strategic study, involving detailed consultation with many stakeholders with an interest in groundwater resources. Such balances are not easy to achieve because groundwater systems are complex to analyse and slow to respond to change, resulting in considerable uncertainty in assessment and prediction without in-depth research and high-resolution monitoring. Current institutional and regulatory arrangements for the water sector in England and Wales do not appear to be achieving the best possible use of aquifer storage and optimal investment in groundwater protection.     

EARLY ARAB WATER TECHNOLOGY IN SOUTHERN SPAIN

This paper describes many of the ways by which the Arabs in southern Spain, during their eight hundred years occupation. raised, stored and distributed water without pumps, reservoirs or pipelines. The technology which they used in their water mills was simple but ingenious and differed from that evolving in Britain at that time. Using contourhugging open channels, the Arabs transferred snowmelt from the sierra over long distances, to recharge the ground above the mountainside villages and sustain the spring flows to their fountains through the year.