Sequential aquifer tests at a well field, Montalto Uffugo Scalo, Italy

Abstract

[1] This paper investigates our ability to characterize an aquifer using a sequential aquifer test in a well field that consists of six wells. During the test, we pumped water out from the aquifer at one well and monitored the water level changes at the rest of the wells to obtain a set of five well hydrographs. By pumping at another of the six wells, we obtained another set of five hydrographs. This procedure was repeated until each of the six wells was pumped. We then analyzed the six sets of hydrographs using the classical drawdown-time, the drawdown-distance, and the drawdown-distance/time methods. Results of the analysis confirm recent findings that the transmissivity estimates vary significantly at early time and stabilize at late time. At late time, the estimated values from all hydrographs are similar overall but vary slightly according to the locations of the pumping and observation wells. In contrast, storage coefficient estimates stabilized rapidly to distinct values associated with the well locations. We subsequently used a hydraulic tomography approach to include all hydrographs from the sequential aquifer test to estimate the spatially varying transmissivity and storage coefficient fields. The estimated fields appear to be realistic: They reflect the geologic setting and the behaviors of the well hydrographs, although more definitive confirmation is needed.

Joint interpretation of sequential pumping tests in unconfined aquifers

“…This implies that the effective parameters estimated from all the data sets from the pumping tests conducted at A1, A5, and A9 are not the same as the effective parameters for the pumping test conducted at A3. In other words, the effective parameters for the equivalent homogeneous medium are scenario dependent (varying with the geology near the pumping well) as observed and discussed by Straface et al [2007] Sun et al, submitted manuscript, 2012) for pumping tests in confined aquifers. The complex spatial distribution of the parameter cross correlation with the head in the unconfined aquifers presented in the study by Mao et al [2013] further elucidates such a scenariodependent nature of the effective properties.…”

“…Traditional characterization approaches have adopted homogeneous conceptual models that assume aquifer homogeneity and have attempted to derive effective hydraulic parameters based on drawdowns from a single pumping test, for example, those by Theis [1935] and Cooper and Jacob [1946] for confined aquifers and those by Boulton [1963], Dagan [1967], Brutsaert [1970], Streltsova [1972aStreltsova [ , 1972b, Neuman [1972], Lakshminarayana and Rajagopalan [1978], Moench [1995], Mathias and Butler [2006], and Mishra and Neuman [2010] for unconfined aquifers. Recent numerical, sandbox, and field experiments by Wu et al [2005], Straface et al [2007], Xiang et al [2009], Wen et al [2010], Huang et al [2011], and Berg and Illman [2011b] however questioned the representativeness of the estimates from these conventional approaches.…”

“…They include numerical studies [e.g., Gottlieb and Dietrich, 1995;Yeh and Liu, 2000;Bohling et al, 2002;Yeh, 2005, 2006;Fienen et al, 2008;Ni and Yeh, 2008;Castagna and Bellin, 2009;Xiang et al, 2009;Liu and Kitanidis, 2011], followed by laboratory sandbox studies [e.g., Liu et al, 2002;Brauchler et al, 2003;Illman et al, 2007;Liu et al, 2007;Illman et al, 2008;Yin and Illman, 2009;Illman et al, 2010;Berg and Illman, 2011a;Illman et al, 2012] and then experimental field studies [e.g. Bohling et al, 2007;Li et al, 2007;Straface et al, 2007;Cardiff et al, 2009;Illman et al, 2009;Berg and Illman, 2011b;Brauchler et al, 2011;Huang et al, 2011]. All these studies have consistently shown that transient HT can identify not only the pattern of the heterogeneous hydraulic conductivity field but also the variation of specific storage.…”

Rapid field application of hydraulic tomography for resolving aquifer heterogeneity in unconsolidated sediments

“…To account for the nonuniqueness issue the hydraulic parameter field is treated as an outcome of a stochastic spatial process, whereby the mean parameter distribution is reconstructed by matching the observations from the pumping test responses. Straface et al [2007] used this inversion scheme for depth integrated reconstruction of hydraulic conductivity and specific storage fields. However, the reconstructed hydraulic conductivity and specific storage tomograms showed no correlation among each other, which is expected in natural sedimentary aquifers [e.g., Bayer et al, 2011], and no additional field data were provided to support the tomograms.…”

“…[9] Straface et al [2007] published the first field hydraulic tomography application that exploits the potential of geostatistically based inversion. The applied procedure relies on the sequential successive linear estimator (SSLE), as proposed by Zhu and Yeh [2005].…”