Estimating Parameters for your Bore
Pump tests or aquifer tests are carried out to determine how much groundwater can be taken from a bore and to provide information on the potential effects of a groundwater take, for example on neighboring bores or surface water flow. If you are applying for a resource consent to take groundwater, in most cases a pump test is required to assess the effects of taking water.
Two types of pump tests are often undertaken:
A step test is used to assess how much water can be physically taken from a bore and its performance. The test involves pumping the bore at a low rate and then increasing the pumping rate in steps towards the maximum flow rate. While the bore is being pumped, the water level is measured in the bore itself.
A constant rate test (usually 24 hours of pumping) is undertaken to provide information on the aquifer properties and the potential effects of the new take, for example on neighboring bores and streams. The bore is pumped at a constant rate, usually at or above the proposed rate of take and the water level is monitored in the pumping bore and in neighbouring bores.
1. Undertaking the Pump Test
Pump tests can be carried out on new bores or for existing bores where a resource consent is being applied for or if changes are being made to an existing consent.
Often if you are drilling a new bore, the driller will carry out the pump test for you and can provide us with the data to analyse. We can liase with the driller regarding the appropriate tests to carry out.
A constant rate test involves pumping the bore for a set period, usually 24 hours and monitoring the level in the bore during the test and for 24 hours after the test (the recovery). If your bore is near a river or stream we recommend that you carry out a 72 hour test as this provides better data that can be used to assess the effects on surface water. During the test, the water level in neighbouring bores is also monitored (ideally 2 neighbouring bores).
A step test can also be carried out, the main purpose of a step test is to assess how much water can be taken from the bore. This test is not generally required for the consent application but can be used to determine the rate that the constant rate test is carried out and the rate of take for the bore.
2. Analysing the Data
Once the pump test has been carried out we can analyse the data for you to determine the parameters for the bore and the aquifer. These parameters can then be used to model the effects of your water take on neighbouring bores and on surface water. We will provide a report with this information to be lodged with your application.
The data from neighbouring bores is used to model the effects on surface water. To obtain better drawdown data in neighbouring bores, a 72 hour test may be required.
How do I know which Neighbouring Bores to Monitor?
Give us a call and we can help you decide which bores to monitor during your test. Ideally your neighbours won’t be using their bores during the pump test, regardless of whether you are monitoring their bores or not as this can affect the results.
What if your neighbour won’t let you monitor their bore?
It is in your neighbours best interest to let you monitor their bore, as it will provide more reliable data that will be used to monitor the long term effects on their bore. However if they refuse, we will still need to consider the effects on their bore for a resource consent application and the effects can be estimated using modelling.
3. Where do I Start?
Give us a call at Allegrow and we can talk you through the process:
- Obtain resource consent to drill a bore (if the application is for a new bore) – often the driller will do this for you
- Drill the bore (if the application is for a new bore)
- Decide who will carry out the physical pump testing (driller, or Allegrow can recommend)
- Decide what testing is required, step test, constant rate (24 hour or 72 hour)
- Decide which neigbouring bores to monitor and obtain consent from bore owners
- Undertake the pump test
- Provide the pump test data, bore logs and information on the pump test to Allegrow to analyse
- Allegrow provides a pump test report and prepares an assessment of environmental effects to submit with the application.
4. Monitoring Neighbouring Bores
During a constant rate test it is reccommended that you monitor at least two bores, in addition to the pumping bore. Allegrow can help you to find appropriate monitoring bores based on their location and depth and whether they are in the same aquifer as the pumping bore. It is useful to monitor at least one bore in the same aquifer as the pumping bore, and to monitor bores in a shallower aquifer, if available. This provides information on the connection between shallow and deep aquifers and also the potential for effects on stream flows. We can provide information on neighbouring bores, but you will need to visit the owners of the bores to get their permission to be monitor their bore during the test. The monitoring bores should not be pumped during the constant rate test and should also be switched off beforehand in enough time for the water levels to stabilise and recover. If there are other bores pumping nearby that might affect the results of the constant rate test, these should also ideally be switched off prior to, and during, the constant rate test. In practice, this may not be possible or you may find that the nearest bores cannot be monitored. If this is the case you can try to find suitable alternatives or, for example it could be an option to undertake the constant rate test during winter when less pumping for irrigation occurs, avoiding periods where water may be used for frost protection if there are orchards nearby.
Effects on Neighbouring Bores
The data obtained from the constant rate pump test can be used to determine the effects on neighbouring bores. The data is used to obtain parameters for the bore and aquifer and these are used to predict the drawdown in neighbouring bores. Depending on how deep the neighbouring bores are, the available water in the bores and the predicted drawdown an assessment can be made as to the scale of effects. If the effect is considered to be minor it is not necessary to consult with the neighbours.
If the effect is considered to be more than minor then consulting with the neighbours and obtaining written approval is generally required to avoid the application being limited notified and potentially going to a hearing. If you are in this situation we can help you with some options to consider to reduce the potential effect on neighbouring bores.
Effects on Surface Water
Taking groundwater can intercept water that would normally make its way into surface waterways or increase natural recharge from these waterways. This can lead to what is known as ‘stream depletion’, where flow in surface water flows can reduce as a result of groundwater use. The constant rate test is important to assess the effects on surface water. This is particularly important where the stream is fully or over-allocated and council policy is to decline consent applications. .
Stream flow does not generally need to be monitored during a constant rate test. This is because it is very difficult to monitor stream flows accurately enough to clearly see the effect of pumping and eliminate other factors affecting the stream flow such as rainfall. When undertaken and analysed correctly the results of groundwater monitoring during a constant rate test are normally sufficient to assess the magnitude of a surface water depletion effect for the consent application.
For groundwater bores located near the coast, there is a risk that taking water from the bore can result in seawater being drawn into the aquifer – this is called saltwater intrusion. We can use the parameters obtained from your pump test to determine whether there is a risk of saltwater intrusion into the bore. There are also a number of other ways that we can assess the risk.
If your take is considered to have a risk of saltwater intrusion the council may impose a condition on the consent which requires you to monitor your bore for conductivity which can be used as an indicator of saltwater intrusion.