OGI can design and analyse Pumping Tests.
Pumping Tests are used to establish in situ hydrogeological properties of the ground, providing parameters that are used in designing an efficient dewatering system or geotechnical design.
Pumping Tests can save considerable sums of money by enabling the design of dewatering systems or geotechnical design to be tailored to the ground conditions at the site and to the specific construction project requirements.
Typically a Pumping Test will require the drilling and installation of two or more wells capable of being pumped from. These wells are installed with well casing and an appropriate filter pack. Water is pumped from the “pumping” well and the other well or wells are used as “observation” wells in which the groundwater drawdown is measured.
The drawdown measured in the observation well(s) is (are) plotted against time (See diagram above). When plotted on a log time scale, the bulk Permeability of the ground can be calculated and parameters such as Transmissivity and Storage Coefficient can be calculated.
OGI are able to carry out the following Pumping Tests:
- Falling Head Test
In this test, water is pumped from the pumping well and drawdown over time is measured in the observation wells.
- Rising Head Test
In this test, a well that has been pumped from has the pump switched off and the water level rise with time is measured.
- Constant Head Test
In this test a constant head is maintained in the pumping well and the flow rate is measured.
OGI will design an appropriate pumping test, including well installation details for the specific ground conditions encountered and for the construction project requirements.
Pumping Tests should ideally be carried out ahead of a dewatering system design as the data produced will enable the optimum number of dewatering wells to be installed rather than a conservative overestimate of the required number (saving drilling costs).
Alternatively, Pumping Tests can be carried out in the early stages of a dewatering system installation in order to confirm dewatering system design assumptions, so that any appropriate amendments can be made, again to optimise the design of the dewatering system at an early stage.
OGI’s Pumping Test wells are always designed so that they can be incorporated as part of the final dewatering system, saving on potential well duplication, therefore saving on drilling costs.
The actual well installation can be adapted subject to the geology encountered during the drilling of the wells so as to maximise the yield potential of each well.
Other advantages of carrying out an early stage pump test are that drilling of pumping test boreholes can:
- provide valuable localised site investigation data
- provide a good estimate as to how long it will take to install a full dewatering system
(this can be very important to the Construction Contractor as it enables tighter control when planning critical path operations).