No abstract

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.

Water companies are now required by the Drinking Water Inspectorate to install continuous monitoring for Cryptosporidium at all sources (surface water and groundwater) where there is deemed to be a significant risk of Cryptosporidium oocysts being present in the final water. This has substantial cost implications, not only for the one-off installation of monitoring equipment, but also for the daily collection and analysis of samples. This paper describes a methodology that has been used by Southern Water to screen all their groundwater sources, in order to identify those which are at significant risk of Cryptosporidium contamination, and which therefore need continuous monitoring. The methodology is a semi-quantitative scoring technique, developed by the authors, which produces a ranked list of sources and enables action to be prioritized. The methodology is designed to operate with a level of information and data easily available to a water company, overcoming the problems of significant data requirements associated with probabilistic methodologies.

The Isle of Wight is a small, heavily populated island, where complex and careful management is required to ensure sustainable use of water resources. Much of the island is underlain by permeable strata and groundwater is an important source of supply. Many groundwater studies were undertaken by the water provider and regulatory authority from the 1970's onwards, but this work is not publically available. This paper reviews these previous studies and provides an overview of the hydrogeology of the island with particular focus on the Lower Greensand Group and the Chalk/Upper Greensand aquifer. As one of the areas in the UK to experience water shortages during the 1976 drought, the Isle of Wight became the focus for new strategies for the sustainable development of water, which included the exploitation of more marginal aquifers, water metering and an engineering solution to provide water from the mainland. Ensuring future water demand is managed sustainably in an area where aquifers are fully exploited is likely to rely on the twin track approach of both further demand-management and unconventional water resource development, such as wastewater re-use or desalination.

Ingress of sand usually occurs in wells abstracting from sandstone aquifers that are poorly cemented. Impacts can be serious and may add significantly to production costs. They include loss of yield and continuity of supply, a reduction in the efficiency and operational life of wells and pumps, more frequent maintenance of wells and ultimately well replacement. The design of high-capacity sand-free wells in sandstone aquifers is often problematical. This is partly because a substantial proportion of the flow is through fractures, which means that well design criteria of screen slot size and artificial pack grain size and grading that have been developed for unconsolidated granular aquifers are not generally applicable. Also, many sandstone aquifers are multi-layered. Interbedded fine-grained and friable sandstone layers or loose sands are often responsible for sand entering a well. Excluding them is often difficult in practice without blocking productive fracture zones, and, therefore, risking a reduction of well yield. Well design alone is not always capable of controlling sand pumping. Pumping at a lower discharge rate, regulating flow at start-up, and the use of sand traps at the ground surface or inside wells are other measures that can assist in alleviating the problem.