Field Study of Hydrogeologic Characterization Methods in a Heterogeneous Aquifer by Matthew Alexander 1 , Steven J. Berg 1 , and Walter A. Illman 2 Abstract Hydraulic conductivity (K ) and specific storage (S s ) are required parameters when designing transient groundwater flow models. The purpose of this study was to evaluate the ability of commonly used hydrogeologic characterization approaches to accurately delineate the distribution of hydraulic properties in a highly heterogeneous glaciofluvial deposit. The metric used to compare the various approaches was the prediction of drawdown responses from three separate pumping tests. The study was conducted at a field site, where a 15 m × 15 m area was instrumented with four 18-m deep Continuous Multichannel Tubing (CMT) wells. Each CMT well contained seven 17 cm × 1.9 cm monitoring ports equally spaced every 2 m down each CMT system. An 18-m deep pumping well with eight separate 1-m long screens spaced every 2 m was also placed in the center of the square pattern. In each of these boreholes, cores were collected and characterized using the Unified Soil Classification System, grain size analysis, and permeameter tests. To date, 471 K estimates have been obtained through permeameter analyses and 270 K estimates from empirical relationships. Geostatistical analysis of the small-scale K data yielded strongly heterogeneous K fields in three-dimensions. Additional K estimates were obtained through slug tests in 28 ports of the four CMT wells. Several pumping tests were conducted using the multiscreen and CMT wells to obtain larger scale estimates of both K and S s . The various K and S s estimates were then quantitatively evaluated by simulating transient drawdown data from three pumping tests using a 3D forward numerical model constructed using HydroGeoSphere (Therrien et al. 2005). Results showed that, while drawdown predictions generally improved as more complexity was introduced into the model, the ability to make accurate drawdown predictions at all CMT ports was inconsistent. Introduction Groundwater flow is controlled by several key prop- erties of the porous media, including hydraulic conduc- tivity (K) and specific storage (S s ). The distribution of these properties will control the migration pattern 1 Department of Earth and Environmental Sciences, Waterloo Institute for Groundwater Research, University of Waterloo, Waterloo, Canada N2L 3G1. 2 Corresponding author: Department of Earth and Environ- mental Sciences, Waterloo Institute for Groundwater Research, University of Waterloo, Waterloo, Canada N2L 3G1; 519-888-4567 ext. 38341; fax: 519-746-7484; willman@uwaterloo.ca Received July 2009, accepted May 2010. Copyright © 2010 The Author(s) Journal compilation © 2010 National Ground Water Association. doi: 10.1111/j.1745-6584.2010.00729.x of contaminants through an aquifer and the drawdown pat- tern in an aquifer hosting a production well. A difficult reality often faced by hydrogeologists is that site geologic conditions are commonly nonideal, due to the presence of significant heterogeneity in geologic media. In general, when trying to predict the behavior of fluid movement in heterogeneous media, it can be said that as the level of het- erogeneity increases, so does the required number of mea- sured data. This was illustrated by Rehfeldt et al. (1992) who suggested that around 400,000 hydraulic conductiv- ity measurements would be required to deterministically model the transport of tracers at the Columbus research site situated in an alluvial aquifer, where K was observed to vary over 3 orders of magnitude. This poses a problem, as every data point requires an investment of time and NGWA.org Vol. 49, No. 3 – GROUND WATER – May-June 2011 (pages 365 – 382) 365