When undertaking construction of a structure that penetrates beneath the water table, dewatering or groundwater pressure relief will be required. To produce a detailed groundwater control design, information on the behaviour of the groundwater and aquifer at the location of the construction project is required. Very often little information is available on the groundwater regime at a particular site. Khansaheb Sykes can undertake test pumping of boreholes in accordance with the Code of Practice for Test Pumping of Water Wells, BS ISO 14686:2003.
Pumping tests are carried out by installing a pumping well and a series of monitoring wells strategically located across the site. The response to pumping is then recorded at the monitoring wells. Carrying out a pumping test obtains the following information:
- The hydraulic behaviour of a pumping well
- The hydraulic properties of the aquifer
- Determines the effects of neighbouring water sources
This gives us the information required to determine the number, spacing and depth of pumping wells required for a successful groundwater control system. The same information is also needed when installing a permanent water well for irrigation or drinking water.
Types of Tests
When undertaking a pumping test, it should be planned to ensure that the maximum information will be obtained about both the water well and the aquifer. Normally five types of tests can be undertaken:
The Equipment Test ensures that the pumping equipment, discharge measuring devices, flow meters, v-notch tanks and water level, monitoring equipment are functioning correctly. It will also allow for the gathering of data to allow planning of subsequent pumping tests.
The objective of the step test is to establish short term yield versus draw-down data. The test comprises pumping the well in a series of steps, each at a different discharge rate. A minimum of four steps is advisable, allowing an estimate of the well’s maximum and sustainable yield. Each step of the test should be equal in duration and for operational and data analysis reasons it is common for steps to be 100 minutes in duration.
Constant Discharge Test
Based on the results of the Step test, the well is pumped at a constant rate over a longer period of time, typically 1 week. The objective of a constant discharge test is to obtain data on the characteristics of an aquifer within the radius of influence of the pumped well. To accomplish this, observation wells will be necessary to determine the aquifer properties.
Constant Drawdown Test
A constant draw-down test is also known as a constant head test and the data is used for the same purpose as a constant discharge test in that it is used for dewatering design and water well testing. A constant head test is suitable for testing when utilizing surface suction pumps and when testing overflowing wells.
At the end of a constant rate or constant head test the pump is turned off and the recovery of the groundwater is monitored. The data obtained is used as a check on transmissivity values derived from the constant rate or constant head test. During a constant rate or constant head test there are variables such as pump performance and power supply that can lead to error. During a recovery test the rate of recovery is only dependant on the natural characteristics of the aquifer, giving good data.
If you are undertaking a construction project or installing a permanent water well and require more information on the groundwater regime at your site, please contact us to for information on undertaking a pumping test at your site. Our technical staff are available to discuss the most appropriate testing for your site.
As a dewatering contractor, we are able to incorporate a pumping test in our complete dewatering contract package by undertaking a pumping test during the installation of our dewatering system to show a saving on the project when possible and highlight potential problem areas at the site.
Khansaheb Sykes LLC are able to undertake test pumping of water wells in accordance with the British Standard BS ISO 14686:2003. Information required when tendering for these works are as follows:
- Site location plan
- Borehole and observation wells site plan
- Borehole diameters
- Total depth of well
- Depth of water
- Distance to discharge point
- Expected flow rates
- Duration of pump test
We will provide you with a complete data report based on the pumping tests carried out, so that you have all the information you may need to carry out your works, and so that we can design the most cost-effective dewatering system. We use small, automatic data loggers that record all the necessary data independently over time. We can provide graphs and reports for your records.