TESTING OF BOREHOLES

To sustainably use your borehole and aquifer system.

OUR SERVICE OFFERING COVERS THE WHOLE OF SOUTHERN AFRICA
Aqua Earth in business since 2002

TESTING OF BOREHOLES

We have looked at the drilling and construction of a borehole, but the borehole is not yet complete. Certainly one of the most important factors concerning one’s borehole is now on hands. How much water can I pump over the long term without drastically affecting the yield and making sure that the borehole is not pumped dry? It should be stated clearly that a borehole test where only the yield and no water levels has been measured does not mean anything in terms of borehole yield (strength), and is at best a test of how the pump equipment performs.

Important Criteria

There are a number of aspects that needs to be taken into consideration when testing a borehole. According to Prof van Tonder at the Institute for Groundwater Studies (Free State University) there are two important rules that needs to be kept in mind when determining the sustainable yield I.e.: The total abstraction from a borehole should be less than the natural groundwater recharge, and secondly, a borehole should be pumped in such a manner that the water level never reaches the position of the main water strike (normally associated with a fracture). Should this happen the yield will inevitably be affected and the borehole would eventually dry up.

Specific information is required to properly test a borehole, these can be listed as follows: what is the rest water level before the start of the test, how does the water level change over time once pumping has started, how long does it take for the water level to recover after the pump has been stopped to recover to the original level – or how far does the water level recover after the same amount of time allowed as for pumping – leaving a residual drawdown.

Water Quality

An important aspect of a borehole yield test is the monitoring of the water quality as pumped from the borehole. A water sample is generally taken at the start of the test as well as at the end of the test for full chemical analysis, while the electrical conductivity and temperature is normally monitored with the water level for the duration of the test.

These information assists in understanding the aquifer behaviour e.g. are we abstracting some of the older water from deeper formations or does the aquifer yield sufficient fresh water quantities? The determination of a sustainable yield will normally take this information into account. The water quality is also of importance to determine whether it is suitable for domestic, irrigation or industrial purposes. An example of this importance for domestic purposes is the nitrate content of water. According to South African Standards the maximum allowable limit is 10mg/l. Too much Nitrate has a major impact on infants less than 6 months old and leads to a condition called methemoglobinemia (blue-baby syndrome) and could be fateful.

Important Criteria

There are a number of aspects that needs to be taken into consideration when testing a borehole. According to Prof van Tonder at the Institute for Groundwater Studies (Free State University) there are two important rules that needs to be kept in mind when determining the sustainable yield I.e.: The total abstraction from a borehole should be less than the natural groundwater recharge, and secondly, a borehole should be pumped in such a manner that the water level never reaches the position of the main water strike (normally associated with a fracture). Should this happen the yield will inevitably be affected and the borehole would eventually dry up.

Specific information is required to properly test a borehole, these can be listed as follows: what is the rest water level before the start of the test, how does the water level change over time once pumping has started, how long does it take for the water level to recover after the pump has been stopped to recover to the original level – or how far does the water level recover after the same amount of time allowed as for pumping – leaving a residual drawdown.

Costs

As mentioned in beginning of this series the perception is that it is too expensive to test a borehole. But is this the case? Remember that the pump supplier can only work on the information that the owner of the borehole provides and can thus not be held responsible for pump or borehole failures if the borehole is over pumped. Either of these incidents might lead to a possible over-capitalization on the borehole equipment with a variety of pump protection devices, as well as additional costs for refurbishing and re – installation of a damaged pump.

In many cases the continuous over pumping of a borehole will lead to the eventual complete failure of the borehole resulting in a requirement to have the borehole re–drilled.

Hydrogeologists are specifically trained to apply the science of hydrogeology in determining the sustainable yield of a borehole and could assist in reducing your risk of borehole and pump failures as well as optimizing the operational costs.

These information assists in understanding the aquifer behaviour e.g. are we abstracting some of the older water from deeper formations or does the aquifer yield sufficient fresh water quantities? The determination of a sustainable yield will normally take this information into account. The water quality is also of importance to determine whether it is suitable for domestic, irrigation or industrial purposes. An example of this importance for domestic purposes is the nitrate content of water. According to South African Standards the maximum allowable limit is 10mg/l. Too much Nitrate has a major impact on infants less than 6 months old and leads to a condition called methemoglobinemia (blue-baby syndrome) and could be fateful.

Groundwater Management/Legalities

We have concluded with a review of different groundwater development phases. All these phases obviously takes place within a certain legal framework and any series on groundwater would not be complete without a look at the legal environment. It is not possible to discuss all aspects of the South African Water legislation in an article such as this, but we are going to look at some fundamental principles, which might affect the local borehole user, as well as other farming activities.

Aqua Earth's Involvement In Groundwater Management

Through our specialist capabilities we are able to provide aquifer management services to local municipalities and mines. These services include from very basic monitoring and reporting services, to high level pump schedule management, remote controll and monitoring and on site training. Talk to us about your specific needs in order for us to assist in developing tailor made monitoring, managing and training program

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Borehole Testing