Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | AUGUST 2015 | 39 but selecting the right screen (and gravel/ lter pack) is absolutely critical to the long term performance and success of the borehole. Finally, the permanent pumping equipment and headworks is installed ready for the borehole to be commissioned and brought into service. Understanding your borehole The majority of the licensed independent water supplies in the UK were constructed before 1940. For those companies using such independent supplies, there is a real commercial need to protect this business critical resource and protect boreholes from failure. The rst step to understanding your borehole is to understand the hydrogeology and the target aquifer that is providing the water. This might comprise a desk study to highlight potential problems with yield and water quality, based on readily available geological and hydrogeological information. The outcome should be an initial conceptual model and risk assessment of the borehole in the context of the wider geo-environmental setting, which if necessary can then be tested, reviewed and validated using data obtained from invasive investigations. O„ en, the next step is to venture down the borehole itself. Geophysics will provide important information about the formation and in† ow, from which it is possible to identify the principal † ow horizons and diˆ erences in water quality. This provides site speci c data that should then feedback to the initial conceptual model and be used to update the risk assessment. A camera survey will provide down-hole images of the engineering condition of the borehole, from which decisions to replace pumping equipment or carry out maintenance can be made. The mode of pumping should also be reviewed to ensure that the borehole is delivering the required volumes of water in the most eŠ cient and cost-eˆ ective manner. Rejuvenating a borehole Without carrying out routine maintenance, there is no way of knowing when a borehole could fail, and fail they do, sometimes overnight, and at other times more gradually. The failure of a pump is a common problem which will result in a temporary loss of supply which although inconvenient, can usually be replaced quickly. Borehole pumps have a life expectancy In the know Technically speaking: boreholes Geophysical logging of a borehole, courtesy of European Geophysical Services in the region of ten years. Structural problems with the borehole itself are much more serious. Modes of catastrophic failure generally involve the collapse of casings or screens, rendering the borehole unusable. Fortunately, such events occur relatively infrequently. Common problems with boreholes develop much more gradually and result in decreased performance and higher operating costs, rather than a sudden failure. Does your borehole need some love? Having worked in the independent water supply industry for over 25 years, Envireau has worked on projects involving new and historic boreholes all over the UK and across the globe; yet o„ en, the most surprising aspect upon arriving at a new site for the rst time is to learn how little a company knows about their water supply. The engineering manager knows exactly how water is used in the processes; the quality of water required is understood; but few question the age of the borehole, depth, diameter and water levels. The secret, underground world of the borehole is o„ en regarded as a black art; best le„ alone. A sound understanding of borehole design and construction and the hydrogeology of the site, followed by routine monitoring and maintenance, is usually all that is required to ensure continued service and sustained performance.

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