Some notes on borehole inspection cameras

These devices have saved me many hours of work. If a borehole has lost some of its original depth, or is producing muddy water, it may be possible to rehabilitate it – but we don’t know exactly what is down there until we look.

The camera I am using is on a reel 100m long with a fish eye lense surrounded by lighting that is directed vertically down the hole. The video we capture can be saved for later viewing.

Water which is allowed to settle in a borehole is normally sufficiently clear to permit visibility below the surface, though neutrally buoyant substances (such as algae) and oily liquids on the surface of the water can be a problem. We also encounter the odd live frog or dead rat – and plenty of insects. The headworks of boreholes really do need to be properly closed off to exclude plants, animals, surface water and light.

If a hole is not cased to the bottom, we may learn something about the geology – fractures, decomposed rocks and formation changes are all visible – as is flowing water. This can be useful in determining whether to deepen a hole.

Older boreholes are cased with steel pipes which corrodes, particles of rust can damage pumps and are a potential health hazard. Many steel cased holes are beyond redemption, but they can often be flushed out with compressed air and re-cased with a smaller diameter PVC casing. We inspect the origional casing looking for breaks or distortions which may prevent the insertion of a second casing.

Most of the holes we inspect are collapsing – slowly. This can be caused by a few things including the casing is not as deed or as strong as it should be, or the annulus between the casing and the side wall has been inadequately backfilled, sediment is entering the hole and probably being drawn into the pump. If sediment accumulates to the level of the pump then the pump may be lost.

Borehole maintenance is important

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