Cost-Effective Hydraulic Tomography Surveys for Predicting Flow and Transport in Heterogeneous Aquifers

Abstract

This study shows how a cost-effective hydraulic tomography survey (HTS) and the associated data estimator can be used to characterize flow and transport in heterogeneous aquifers. The HTS is an improved field hydraulic test that accounts for responses of hydraulic stresses caused by pumping or injection events at different locations of an aquifer. A sequential data assimilation method based on a cokriging algorithm is then used to map the aquifer hydraulic conductivity (K). This study uses a synthetic two-dimensional aquifer to assess the accuracy of predicted concentration breakthrough curves (BTCs) on the basis of the Kfields estimated by geometric mean, kriging, and HTS. Such Kfields represent different degrees of flow resolutions as compared with the synthetically generated one. Without intensive experimentsto calibrate accurate dispersivities at sites, the flow field based on the HTS Kfield can yield accurate predictions of BTC peaks and phases. On the basis of calculating mean absolute and square errors for estimated K fields, numerical assessments on the HTS operation strategy show that more pumping events will generally lead to more accurate estimations of Kfields, and the pump locations need to be installed in high Kzones to maximize the delivery of head information from pumps to measurement points. Additionally, the appropriate distances of installed wells are suggested to be less than one-third of the ln(K) correlation length in x direction.

Joint interpretation of sequential pumping tests in unconfined aquifers

“…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. More importantly, the hydraulic property fields estimated by HT have been demonstrated to yield much better predictions of flow and transport processes than conventional characterization approaches [see Yeh and Zhu, 2007;Ni et al, 2009;Huang et al, 2011;Illman et al, 2012]. Recent work by Berg and Illman [2011b] further substantiated the robustness of HT for a highly heterogeneous geological medium with a variance of log hydraulic conductivity of 5.4 and a vertical correlation scale of 0.15 m. Thus, the call for changing the way we collect and analyze data for characterization of aquifers by Yeh and Lee [2007] appears to be well founded.…”

Prediction of solute transport in a heterogeneous aquifer utilizing hydraulic conductivity and specific storage tomograms

“…However, as pointed out in the theoretical study by Ni et al . [], even if a homogenous model can provide an appropriate fit, it will not capture the scale‐dependent increase of dispersion with transport distance [see, e.g., Molina‐Giraldo et al ., ; Gelhar et al ., ]. In contrast, by reconstructing transport‐relevant structures, their effect on macrodispersion is explicitly simulated, and thus the heterogeneous model is more suited for predicting solute transport along shorter or longer distances.…”

“…Similarly to Ni et al . [], we also compare the BTC prediction by reconstructed model to that of a homogenous one.…”

Stochastic modeling of flow and conservative transport in threedimensional discrete fracture networks

“…Similar to the flow simulation, the depth-averaged conservative solute transport equation for saturated fractured porous media is governed by the ADE and can be written as (e.g., Dagan, 1989;Ni et al, 2009;Zheng and Bennett, 2002): 25…”