To abstract groundwater at a sustainable rate, it is crucial not to stress, harm or ultimately dewater your groundwater resource. It is essential to get a sustainable yield recommendation, which is achieved through pump tests. Various approaches have been considered to adequately determine a safe abstraction yield and will briefly discussed below.
When performing a calibration test, the aim is to firstly get a general understanding of how much water the borehole can deliver. A pump is inserted into the borehole and the initial volume pumped out is kept to a minimum, which is done for approximately fifteen (15) minutes and repeated three (3) times with an increased pumping rate. This ultimately assists to define the general character of the borehole.
The step test comprises of four (4) different rates pumped at sixty (60) minute intervals, increasing the yield / volume of pumping after each interval. The main aim of the step test is to determine a yield for abstraction to do a constant test on for a period of twelve (12) to twenty-four (24) hours. Ideally, if a borehole’s water level can lower towards the fracture depth during the step test and ultimately dewater up to depth of pump installation, one can better assess and determine the constant test rate.
The constant test is conducted ideally for twenty-four (24) hours to determine how the borehole reacts to the abstraction with a yield determined through the calibration and/or step test. After a successful step test, a depth is identified up to where the water level of the resource should not be lowered to. During the constant test, the water level should preferably reach this level close to the end of the twenty-four (24) hour test.
Recording and capturing of the water level and pumping rates at pre-defined intervals is crucial as this ultimately is inserted on a model that assists with an accurate safe yield recommendation. This model is ultimately designed with built-in formulas to aid in a safe yield recommendation.