īy normalizing the distance between observation and pumping wells (t/r²), composite plots show data from fully penetrating observation wells matching the same Theis (1935) type curve or the same Cooper and Jacob (1946) straight line when the aquifer conforms to the Theissian model (Figure 5). The composite plot, another tool for analyzing data from multiwell pumping tests, displays drawdown as a function of t/r² where t is time since pumping began, and r is radial distance from pumping well. Estimation of aquifer properties by matching Cooper and Jacob (1946) solution to distance-drawdown data collected in three fully penetrating observation wells after 2045 minutes of constant-rate pumping in an unconfined aquifer (data from USBR 1995). A single drawdown measurement per well, each recorded at the same time, is plotted on a distance-drawdown graph.įigure 4 shows the estimation of aquifer properties from distance-drawdown data collected at the end of a constant-rate pumping test in an unconfined aquifer using the Cooper and Jacob (1946) straight-line solution. Distance-Drawdown Analysisĭistance-drawdown plots (drawdown versus radial distance) are used to estimate aquifer properties from pumping tests with more than one observation well. The derivative shown on the plot (crosses) guides the fit of the straight line to drawdown data from the infinite-acting radial flow period (data from Walton 1962). Estimation of aquifer properties by matching Cooper and Jacob (1946) straight-line solution to time-drawdown data (squares) collected in an observation well during a constant-rate pumping test in a nonleaky confined aquifer. 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). 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. Estimation of aquifer properties by matching Theis (1935) type-curve solution to time-drawdown data collected in an observation well during a constant-rate pumping test in a nonleaky confined aquifer (data from Walton 1962). distance-drawdown analysis (s versus r).Common methods of interpreting constant-rate pumping tests include the following:
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