Blow yield isn't pump yield

The compressor blew water at lunchtime. By three the client is back at the gate with a pump on the bakkie, wanting a number today.

A factory borehole in Aliwal North. Properly tested, it gives eleven and a half thousand litres a day. The factory needed thirty thousand. A pump on the blow yield: six times too big.

A blow yield is the bucket you filled in a minute. It's not the tap that runs all day. In fractured rock the safe rate is often a third to a quarter of what the compressor blew.

The quick farmer test isn't the answer either. GEOSS tested twenty holes both ways. On average it told the client he could pump more than double the proper rate.

A proper test has three parts. Steps at rising rates, a constant-rate run of a day or three, then recovery. A hydrogeologist signs the number, not you.

Then size the pump on the duty water level, not the rest level. On a farm near Kariega, that was forty-nine metres more lift.

Keep the pump off the quote until the recommendation comes. A replacement pump runs seven to thirty thousand rand. When one burns out, a signed report you didn't write protects you.