Plume Behavior for Petroleum Hydrocarbon in a Tropical Sand Tank: Laboratory Experiments and Scenario-Specific Modelling OLUWAPELUMI O. OJURI AND SAMUEL A. OLA Department of Civil Engineering, Federal University of Technology, Akure, Ondo State, Nigeria Numerical simulations were performed to assess the reactive transport and natural attenuation of gasoline fuel components in a 3-D sand tank model. The conceptual model includes a residual gasoline source that dissolves into the 3-D aquifer. The analysis reveals high to very high correlation between the observed and simulated values (average R 2 ¼ 0.97). A retardation factor R ¼ 1.5, and first-order decay rate of 0.0002=day were obtained from the model calibration for BTEX. The results are highly relevant in the light of the increasing awareness of the precarious trend of lack of monitoring and remedial feasibility data for the subsoil environment in the thousands of gasoline fuel stations, and petroleum storage= distribution underground infrastructure and the riverbeds of inland waterways in Nigeria. The biodegradation rate was the most sensitive model parameter, with about 82% increase in BTEX maximum plume concentration, for the zero biodegradation scenario. Keywords aquifer model, BTEX, modelling, natural attenuation, reactive transport 1. Introduction This research involves the design and implementation of a quasi-natural gradient, laboratory scale aquifer model experiment for the transport of petroleum hydro- carbon (organic compounds) in groundwater. Achieving the goals of this experiment requires analyses of the experimental data base to obtain information about the porous media properties and the movement of the petroleum hydrocarbon (Organic compounds) in time and space. Such information is especially important in quantify- ing the relative mass loss and apparent retardation of the petroleum hydrocarbon organic solutes; benzene, toluene, ethlybenzene and xylene (BTEX), and in attempt- ing to validate mathematical models of advective-dispersive transport. Contaminated soil and groundwater poses a serious problem with respect to soil= ground water quality and the risk of spreading pollutants into other compartments of Received 28 May 2009; accepted 8 March 2010. The authors would like to acknowledge the funding by the Federal University of Technology, Akure, Ondo State, Nigeria. University research grant URG=MAJOR=2006= 16, and the coding of numerical algorithm in FORTRAN by Babatunde J. Abiodun. Address correspondence to Oluwapelumi O. Ojuri, Department of Civil Engineering, Federal University of Technology, Akure, Ondo State, Nigeria. E-mail: ojurip@yahoo.com Marine Georesources and Geotechnology, 28:154–172, 2010 Copyright # Taylor & Francis Group, LLC ISSN: 1064-119X print=1521-0618 online DOI: 10.1080/10641191003785053 154