Abstract
Currently slug tests in South Africa are used with two objectives in mind: • To get a first estimate of the yield of a borehole • To estimate the K-value (or T-value) of the aquifer near the borehole. The paper shows that the use of currently available slug-test interpretation methods to analyse slug tests in fractured-rock aquifers to estimate a T or K-value is problematic. The estimated value is dependent on the flow thickness (thickness of the part of the aquifer in which flow occurs due to the slug input). If this thickness of flow is known, the estimated T-value is more representative of that of the fracture zone. By using the total thickness of the formation for the estimation of the K-value in slug-test analysis, the estimated K-value (and thus KD-value) does not represent the T-value of the formation. Water SA Vol. 31 (2) 2005: pp.157-160
Highlights
In performing a slug test, the static water level in a borehole is suddenly lowered or raised
The paper shows that the use of currently available slug-test interpretation methods to analyse slug tests in fractured-rock aquifers to estimate a T or K-value is problematic
The estimated value is dependent on the flow thickness
Summary
In performing a slug test, the static water level in a borehole is suddenly lowered or raised. In South Africa slug tests are conducted for the following two reasons: To estimate the hydraulic conductivity (K) of the aquifer in the vicinity of the borehole To get a first estimate of the yield of a borehole (Vivier et al., 1995). A major characteristic of the main aquifer is the presence of a horizontal fracture that coincides approximately with the centre plane of the sandstone layer, and which intersects all 11 boreholes with significant yields on the Site, of which UO5 is one. Measurements were taken in the observation borehole UO6 These pumping test data were analysed with a numerical 3D model (Van Tonder et al, 2001), and the following parameters were estimated (Table 1):. Note that a flow thickness of 30 m will indicate the depth from the water level to the end of the borehole and that a thickness of 0.16 m is the thickness of the fracture zone in borehole UO5
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