Groundwater sources are typically long-life assets. However, they can be at risk of failure if their performance is not monitored and appropriate maintenance regimes adhered to. In addition, sources that have lain dormant for some time may also require some rehabilitation before they can be put back into service.
For operational sources failure can come about in a number of ways. It may be water quality failure such as high levels of microbiological or chemical contaminants; excessive pumping of sand; well failure such as caving in of the bore; or progressive loss of performance through encrustation or biofouling. Understanding the current condition of the borehole, its history, and the conceptual model of the groundwater system that supplies it are key in being able to predict the future performance of the source and an appropriate maintenance regime.
As groundwater specialists, we have a wealth of experience in, and understanding of, groundwater systems and assets of a number of the UK water companies. In addition, we are experienced in borehole condition assessment and understand the latest water industry guidance and methodologies for assessing failure risk and evaluating maintenance cost benefit. As an example, we have recently been involved in reviewing Thames Water’s groundwater source records to help prioritise future monitoring. We have also reviewed a number of their sources to try to determine the predicted performance profile and assess a number of maintenance scenarios to determine the most cost effective one. For Severn Trent Water Limited we assisted in the preparation of drinking water safety plans which included on and off site inspections and review of water quality data.
For dormant sources the first step (assuming abstraction licensing is not an issue) is assessment of the condition and performance of the bore. In the first instance this would comprise a visual inspection of the wellhead to confirm structural integrity, sanitary seal, and requirements for further testing. This is likely to be followed by downhole condition survey – usually CCTV and possibly other forms of downhole logging as appropriate. In order to confirm the well performance well testing would then be carried out.
ESI, now part of Stantec, has experience in drawing up the specifications for groundwater source condition assessments and testing, and in interpreting the results.