Analysis of pumping test data for determining unconfined-aquifer parameters: Composite analysis or not?

Abstract

Recently, composite analysis (CA), which simultaneously analyzes all drawdown data from multiple observation wells, has been applied to determine the hydraulic parameters of an unconfined aquifer. Moench (1994) claimed that the value of specific yield (S (y)) determined from non-composite analysis (nonCA) is sometimes unrealistically low as compared with that obtained by water-balance calculation, and results from CA are better representative of aquifer properties than those from nonCA. To examine the validity of this assertion, the drawdown data from a pumping test conducted at Cape Cod, Massachusetts, USA, were analyzed using both nonCA and CA methods. The results show that the mean estimates of hydraulic conductivity and S (y) determined from CA are close to those determined from nonCA. In some cases the analysis based on CA also results in low estimates of S (y) as compared with those determined based on nonCA. A hypothetical case study is presented, which examines the effect of measurement errors on the estimated parameters. The results indicate that the CA method also gives poorer estimates of S (y) than the nonCA method if the pumping test data contain measurement errors. Moench AF (1994) Specific yield as determined by type-curve analysis of aquifer-test data. Ground Water, 32(6):949-957.