Sand in the Hole!

[Olieboer]

A tale that bears out what my father used to tell me... "You're better born lucky than rich, son!".

As a temporary measure we wanted to re-commission an long un-used 4 inch water well to provide irrigation water to vegetables and herbs in the field below the property. The plan was to run a 0,5hp submersible pump to feed a 1 inch line to the field. The well is due to be covered by the foundations of a new house, but would cover the irrigation needs over the winter.

The necessary materials were brought to site and work began...

After running the hard 1 inch irrigation tubing into the well, the hold-up-depth was measured at 17m with a soft, silty bottom. The pump was run on dual steel winch lines and suspended about 1m above HUD to leave a 'sump' in case of additional silt ingress. This would eventually prove to be totally inadequate!!

The static water level was seen at about 6-7m which would give a good positive suction head of nearly 10m to the pump, so without further ado the pump was started up to roughly gauge inflow performance. My lady and I chortled happily as good, steady flow emitted from the 1 inch testing line. It was getting late, the pump was just about to shut down - then the flow stopped. A couple of coughs and spits, then nothing. Pump was (very) quickly shut down (the controller and overload protection still to be installed and commissioned, you see).

Using a laser penlight it was possible to see that the static water level had dropped a great deal in the well. The lines suspending the pump were drum taught, but with a quick session of working them up and down the pump was again free hanging. It seemed as though a plug of loose sand or silt had sloughed in, trapping the pump.

The pump was pulled back a further 1,5m and carefully restarted. Flow restarted almost immediately, but went from turbid to a deep sandy color. Not to beat the pump up too much, it was planned to run no more than a few minutes unless the sand inclusion reduced and good water flow was established. Whether the pump seized first as more sand sloughed in than it could handle, or coincidentally it was turned off by me, is a moot point now. Again, drum tight suspension cables. But see the photo of the produced sand, this didn't bode well and things were looking pretty grim.

After a good deal of heaving (and little cursing) the pump fortunately came free and was wrangled out of the well, oozing sand (see photo). The pump and motor were separated on the bench and the motor turned freely and started up without hesitation. The pump was solid, and was blasted top and bottom with water until about a kilo of sand flushed out. See photo of about half the pump contents laying in the blue bucket! After much flushing/washing of all the components the pump and motor were reunited and ready to run in another well we have. This one has a better production, but will need a longer cable installed to reach it.

Lessons learned:

- The water producing formation was much higher up in the well than expected - above the pump

- Sand production history was not understood, although the well was known to be a fairly poor producer

- Given the first two issues the pump should only have been run a couple of meters into the static water first, not anywhere near the HUD (start top-down, not bottom-up), and then progressively lower.

- Run double suspension lines on all pumps, they cost nothing compared to cost of leaving a submersible down hole...

- Take the time to install and commission the motor control package, don't try a suck-it-and-see test like I did!

I was lucky, very lucky. Thanks Dad, I know just what you mean!