Building Our Pumphouse

After finding the borehole on the farm, we needed to build a pump house to protect the electrical installation from copper and cable thieves.

Developing this old borehole was challenging in its own way. First, we needed someone to test it for us. One of our worries was that it might be dry or no longer working, because a borehole pump had got stuck in the hole.

In our search we came across a local borehole expert who also knew this borehole. He inspected it and found, to our excitement, that it was still working.

There are a number of things to consider when testing a borehole. According to Prof van Tonder of the Institute for Groundwater Studies (University of the Free State), two rules matter most when determining sustainable yield. First, the total abstraction from a borehole should be less than the natural groundwater recharge. Second, a borehole should be pumped so that the water level never reaches the main water strike (normally associated with a fracture). If that happens, the yield will be affected and the borehole will eventually dry up.

Specific information is needed to test a borehole properly:

• the rest water level before the test starts,
• how the water level changes over time once pumping starts,
• how long the water level takes to recover after the pump stops, or how far it recovers in the same amount of time as the pumping lasted, leaving a residual drawdown.

The step test

During this test the pump rate is increased in steps at regular intervals. For example, a borehole may be pumped at 1,000 l/hr for an hour, then at 2,000 l/hr for the next hour, and so on for several more steps. This test is useful for determining how effective the borehole is, but not for its long-term sustainable yield. For that, the constant rate test is more useful.

The constant rate test

In the Constant Rate Test (CRT), the borehole is pumped at a constant rate for 8 to 48 hours or longer; the length of the test is normally proportional to the expected yield and importance of the borehole. Water levels are recorded in the pumping borehole and in any observation boreholes. The time-drawdown data is then analysed to estimate the aquifer's properties and how the borehole responds to pumping, which helps assess its sustainable yield.

After all this testing, the borehole was found to supply 9,000 litres per hour. Because it would only be used for household purposes, it did not need to be registered.

We had the water tested and it looked relatively good. The only problem, unfortunately a big one, is the salts. The Total Dissolved Solids (TDS) of 1,200 mg/L is almost three times that of normal water. We use the water in the house, but we drink bottled water.

On the left in the photo is Patric, our builder.

The finished product