Methods to Determine Storativity of Infinite Confined Aquifers from a Recovery Test

Abstract

Starting from the equations of Theis and Cooper-Jacob, two new mathematical methods are proposed for interpreting the residual drawdown data for an infinite confined aquifer. Under Theis' assumptions and using the Cooper-Jacob approximation, the principal aquifer characteristics of transmissivity, pumping storativity, and recovery storativity are expressed without any correction or additional assumption. An actual case is used for illustration and confirms the validity of proposed equations and methods.

An Improved Straight‐Line Fitting Method for Analyzing Pumping Test Recovery Data

“…All methods listed in Table 1 gave comparable results, which does not enable us to differentiate the performance of these methods. However, the unique features of our approach become obvious when we compare the straight‐line plot in Figure 1 with straight‐line fitting reported by others, e.g., Chenaf and Chapuis (2002, Figures 2 to 5) and Samani and Pasandi (2003, Figure 5b). In our Figure 1, all the points transformed from the recovery data fall onto a straight line nicely except for a couple of late time points, which may be due to measurement errors.…”

“…All other plots reported in Table 1 showed deviation from a straight‐line fit for early‐time data. In fact, both Chenaf and Chapuis (2002) and Samani and Pasandi (2003) adopted the Cooper‐Jacob approximation to arrive at linear relations that require both u 1 and u 2 to be no more than 0.01. For the application described in the previous section, we plotted the values of u 1 and u 2 vs. the corresponding t ′ in a semilog graph (Figure 2).…”

“…Multiple sets of recovery data from multiple wells can be analyzed separately and results compared to test the reliability of each independent estimate. Furthermore, we should note that Chenaf and Chapuis’ (2002) approach made no assumption regarding the storage coefficient during the pumping period being equal to the storage coefficient during the recovery period, which may be important if pumping has caused consolidation of the confined aquifer.…”

“…Department of the Interior (USDI) (1977, p. 120) to estimate T and S . This set of data has been analyzed by others, including Goode (1997), Chenaf and Chapuis (2002), and Samani and Pasandi (2003).…”

Estimation of aquifer parameters from residual drawdowns

“…The same set of data has been analysed by other authors including Ballukaraya and Sharma (1991), Singh (1999), Chenaf and Chapuis (2002), Singh (2003), Zheng et al (2005) and Singh (2006). The residual drawdowns were measured in an observation well located 30 .…”