Is your borehole at risk of collapse?
In the last few years, we have seen an alarming increase of existing boreholes collapsing in the Western Cape. It is important to take speedy action when the first signs become visible. I like to explain some of the pitfalls in dealing with collapsing boreholes, the reasons why boreholes collapse and the signs to look out for.
We are usually only called out to a collapsing borehole when the pump motor burns out or trips repeatedly. The reality of a collapsed borehole is usually an interruption of your water supply with resultant economic consequences, a replacement pump and motor and often the loss of the borehole. If the hole is lost then a new borehole has to be drilled nearby while hoping to get water again. One usually cannot drill in the same spot or right next to it due to the extended pumping of collapsing boreholes where sinkholes were created on the surface.
Boreholes can collapse for different reasons.
The biggest risk factor is if your borehole only has a metal sleeve (pipe). The metal sleeve and rock below from the sides of your borehole. The sleeve will eventually rust through somewhere leading to the borehole collapsing. The general consensus is that metal sleeves are safe for 15 years plus. We are aware of perfectly fine 50 + year old boreholes but have worked on many that were younger. A less well-understood factor might be, changes in underground pressures, possibly affected by changing water levels due to the drought.
Something we also often see in the Cape is boreholes in soft formations that would typically be sleeved with PVC pipe might suddenly be overwhelmed by very fine sand. This fine sand occurs in layers and pockets in some areas. As the borehole is used over time a channel might open up to such a pocket resulting in the very fine sand entering the casing through the slots and overwhelming the pump. Lastly, there could be underground forces or changes that impact onto the casing resulting in equipment getting stuck or worse. In addition, we have had numerous cases where, by accident or sabotage the electrical cable was dropped into the borehole causing it to wedge between the pump and sides of the borehole, thereby jamming the pump.
The signs to look out for is:
Visible signs of rusting on the casing. If it is rusting above the ground then it will be worse below the ground.
Any changes in colour or other indications that a borehole that used to pump clear is now pumping a bit of sand, clay or mud with the water.
Repeated tripping of the pump.
Bits of rust, stones or mud on the pump if it is pulled up
Unexplained changes in yield.
It is quite common to clear out boreholes with compressed air.
We believe that that should never be done if you suspect the borehole might be collapsing. The compressed air rushing up is causing a negative pressure (sucking) on the sides of the borehole. That is why the driller needed the casing in the first place while drilling. Calling a drilling company with a big air drill is a sure-fire way of writing off your borehole. With experience and the right equipment, we can open the borehole while temporarily stabilising the sides chemically, allowing us time to insert a PVC well screen inside the existing borehole.
If you have any concerns about your essential water supply please do give us a call. We are able to come out during lockdown and do work with a bit of extra discount while we are not drilling for our residential customers.