This study presents an approach and a model to evaluate the potential exposure from an episodic chemical spill into a river. The River Dilution Model (RDM) was developed to predict chemical concentrations in a river as a function of the downstream distance and the time after an instantaneous release. RDM is one-dimensional dilution model in an Excel spreadsheet which allows for a quick screening appraisal. RDM predictions showed reasonably good agreement with measured values of peak concentration and arrival time at distances of 3.1-7.7 km downstream of the dye release point. RDM significantly over predicted peak concentrations at greater distances because it did not consider chemical removal processes occurring in the long travel time. This paper describes how to use the predicted chemical concentrations to assess the potential human and aquatic hazards. Several sources of information were identified to define model input and toxicity information. RDM and the approach were applied in a case study to demonstrate how to evaluate the potential hazard for a spill of hydraulic fluid. The approach will enable facilities to assess potential impacts with readily available tools, and then decide which engineering or administrative controls are needed to prevent or manage a chemical spill. (C) 2011 Elsevier B.V. All rights reserved.