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Rehabilitation of an Underperforming Borehole
Borehole Rehabilitation
Kent

A large pharmaceutical manufacturer uses borehole water to supply all their water for processing. Problems had been observed with poor quality water (build up of iron coloured sludge) for many years; requiring pumps and rising mains to be changed at regular intervals.

An analysis of water samples showed that the groundwater contained high levels of dissolved iron and manganese, that appeared to be precipitating and clogging the borehole pump and delivery pipework. A borehole condition survey suggested that the borehole was in generally good condition but iron precipitation and corrosion was occurring principally within the zone of water table fluctuation.

A review of operation pumping data for the borehole suggested that pumping water levels were very close to the pump intake; below the recommended net positive suction head (NPSH). It was considered likely that air was being entrained into the water and exacerbating the precipitation of iron, and corrosion of iron pipework.

To address the problem, a simple programme of borehole rehabilitation was carried out to remove the build up of iron precipitate. An inverter control system was installed to control pump speed and a revised pumping programme implemented; with pumped water levels restricted to a lower level. Whilst some precipitation is inevitable in this case, the extreme problems observed with sludging of pipework has not been observed.

This shows the importance of understanding water chemistry and ensuring pumps are carefully controlled to maximise borehole and pump performance. It also highlights the need for regular monitoring to plan maintenance activities effectively, rather than responding to the problems when they occur.

Image Top Left: Before and after encrustation treatment.

Image Below: Camera survey images showing the removal of encrustation following treatment.

Image Below: Camera survey images showing encrustation of the well screen