A three-dimensional Computational Fluid Dynamics in house model was used to simulate the dispersion of soluble substances in a river. The finite volume method was used to approximate the momentum, mass, and species conservation equations. A Cartesian coordinate system was chosen to represent the river. The Streeter-Phelps model was used to predict the concentration of organic substances and dissolved oxygen along the river. The model could also predict the impact of multiple effluents discharges. The proposed methodology is a good tool for the evaluation of the environmental impact caused for pollutants emissions in rivers. Experimental comparisons for soluble chloride dispersion were made for the Atibaia-River near REPLAN-Paulínia (major petroleum refinery in Brazil). Despite approximations imposed to the shape of the river, the results show good agreement with experimental data. This is an abstract of a paper presented at the AIChE Annual Meeting and Fall Showcase (Cincinnati, OH 1/04/2005).2005 Chow, V.T., (1959) Open-Channel Hydraulics, , McGraw-Hill Book CompanyFischer, H.B., The mechanics of dispersion in natural streams (1967) J. Hydr. Div., 93 (6), pp. 187-216Modenesi, K., Furlan, L.T., Tomaz, E., Guirardello, R., Nunhez, J.R., A CFD model for pollutant dispersion in rivers (2004) Brazilian Journal of Chemical Engineering, 21 (4), pp. 556-568. , October-DecemberNokes, R.I., Hughes, G.O., Turbulent mixing in uniform channels of irregular cross-section (1994) Journal of Hydraulic Research, 32 (1)Rodi, W., (1984) Turbulence Models and their Applications in Hydraulics - A State of the Art ReviewSpalding, D.B., A single formula for the "law of the wall" (1961) Journal of Applied Mechanics, 28, pp. 455-457White, F., (1992) Viscous Fluid Flow, , Mc Graw Hill, 2nd editionTominaga, A., Nezu, I., Turbulent structure in compound open-channel flows (1991) Journal of Hydraulic Engineering, 117 (1). , January