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Introduction This manual describes a computer model for simulating transport of hydrocarbons(HC)in ground water under the influence of oxygen (02) limited biodegradation The model core is based on_the USGS 2- D solute transport model(Konikow and Bredehoett, 1978) Although this manual is self-contained and will allow the user to run BIOPLUME Il easily,it is recommended that the user be familiar with the USGS code beforehand A user-fnendly menu-dnven preprocessor has been built in the code The preprocessor provides the user with three options i)data inputtediting, 2)simulation run performance, and 3)graphical representation of output The model is designed to run on an IBM PCIAT or compatible system The purpose of the simulation model is to compute the concentration of a dissolved hydrocarbon that ' is undergoing biodegradation in an aquifer Changes in chemical concentration occur primarily due to four distinct processes 1) convective transport,in which dissolved chemicals are moving with the flowing ground water,2) hydrodynamic dispersion, in which molecular and ionic diffusion and small scale variations ' in the velocity of flow through the porous media cause spreading of the contaminant front, 3)fluid sources or sinks,such as pumping or injecting wells, and, 4) reactions, in which the concentration of the contaminant may increase or decrease due to chemical and physical reactions within the ground water or between the water and the solid aquifer material ' The standard 2-D USGS code assumes that no reactions occur which affect the concentration of the species of interest BIOPLUME 11, on the other hand, assumes an instantaneous reaction between HC and ' Oz The instantaneous reaction decreases the concentration of HC by an amount that is proportional to the available 02 in the aquifer(t is assumed that 3 units of 02 are required to completely biodegrade 1 unit of HC) B10PLUME II solves the solute transport equation twice,once for HC and once for 02 This allows the simultaneous simulation of two plumes, an HC plume and an 02 plume The two plumes are combined using superposition at every particle move to simulate the reaction between HC and OZ BIOPLUME ll is extremely versatile it allows the simulation of a retarded HC plume undergoing ' biodegradation and it provides the user with the capability to simulate in-situ biorestoration schemes such as the injection of oxygenated water Moreover,the model simulates anaerobic biodegradation and reaeration as a first order decay in HC concentrations 1 I