Constant-Rate Pumping Tests
Typically, aquifer properties are estimated from a constant-rate pumping test by fitting mathematical models to drawdown data through a procedure known as curve matching. Curve matching may be performed using type-curve methods on log-log plots (Figure 2) or straight-line methods on semi-log plots (Figure 3).
Residual drawdown data can be more reliable than drawdown data because the recovery occurs at a constant rate, whereas constant discharge pumping is often difficult to achieve in the field. Residual drawdown data can be collected from both the pumping and observation wells.
Aquifer pumping test guidelines
Pumping tests are carried out to determine how much groundwater can be taken from a well, and what effects pumping will have on the aquifer and neighbouring well supplies. This page gives practical advice on how to carry out a pumping test.
Understanding groundwater aquifer parameters (hydraulic conductivity, transmisivity and storativity for example) is important in site dewatering evaluation. It is beneficial to both Engineers and contractors to have a good understanding about the hydrogeology of a site before designing and constructing a dewatering system. The characteristics of the aquifer confirm if the assumptions included in the dewatering system design meet the project criteria. Griffin has extensive experience conducting aquifer tests including:
In reviewing any such application, the Department must determine if the proposed well(s) will adequately meet the needs of the applicant and if others who may rely on the same aquifer will be adversely affected. The requirements that follow have been designed to produce the accurate and complete information that is vital to these determinations and whether modifications to the application or conditions in a potential permit are required.
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Measurements for both the drawdown and recovery phases, are made with respect to time. The test data can then be analysed to give values of transmissivity, storage coefficient and the yield or specific capacity. The analysis of pumping test data itself is a very vast subject and involves a lot of detailed analysis of the nature and geometry of aquifers and aquitards, their relationship and variability of properties, which must be known before conducting the test.
This report describes the results of a 3 day constant-rate pump test of an alluvial aquifer on the north shore of the South Saskatchewan River in section 6, township 13, range 6, West of the 4th meridian. The purpose of the test was to assess the water-supply potential of the aquifer and, in particular, to determine its suitability for an induced-infiltration supply for the town of Redcliff. Such a supply, if feasible, could yield water in amounts capable of meeting municipal and industrial demands.
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In South Africa, the main aim of pumping tests is to estimate what we call sustainable yield of a borehole. The sustainable yield is defined as the rate at which the borehole can be operated for a long time (e.g. two years) without reaching a specified drawdown level (in other words, the position of the main water strike in a fractured-rock aquifer), including the influence of boundaries and other boreholes.