Bore purging

  • Fact sheet
  • August 2015
Bore Purging

The purpose of groundwater sampling is to retrieve a water sample that represents the characteristics of water below the ground surface.

To obtain a representative sample it is necessary to remove the stagnant water from the bore casing before a sample is taken. This is called purging.

We recommend that at least three columns of bore water be removed and left to refill before sampling. This allows the pH, EC and temperature of the ground water to stabilise, ensuring that the obtained sample is truly representative of the groundwater.

Important: A bore has to be purged before each sampling.

The volume of water to be purged before a sample can be taken depends on the diameter of the bore, as well as the depth of the water column.

Calculate the amount of water to purge

1. Calculate the water column length (total depth–water level):

2. Choose the approximate volume that needs to be purged, per meter, for your bore diameter:

3. Multiply the water column length by the per metre volume. This is the total quantity of water to purge. For example a 100mm (or 4 inch) bore and a water column of 40 meters will require   
    1000L water to be purged: 25 litres x 40 = 1000 litres. 

More information

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