"PREFACE: To assist site or facility managers@ this primer provides brief@ simplified guidance for ""screening"" petroleum release sites for ecological risk to local plants@ animals@ and/or natural habitats. This project was undertaken to provide an elementary companion to the human health component of the Decision Support System for Exposure and Risk Assessment (DSS software program@ API@ 1999). The DSS model estimates site-specific human health risks@ assists in determining the need for site remediation@ and evaluates the uncertainties of model input parameters. This document focuses on ""downstream"" facilities (refining and marketing@ including retail gas stations) and on petroleum products (versus crude oil)@ although the concepts in this primer could be modified and usefully applied to other petroleum industry sites. In this primer@ the goal of the screening process presented is a documented determination of the likelihood of adverse ecological effects. A low probability of adverse effects indicates that no further ecological assessment is warranted; whereas a high probability of adverse effects??or analytical uncertainty??indicates that more detailed analyses may be appropriate. Every effort has been made to focus on a few critical ecological risk assessment elements@ use existing information/data@ and simplify instructions for a preliminary evaluation of ecological risk. When relevant information is unavailable@ or when the site investigator is uncertain in an evaluation@ an expert should be consulted. Internal company environmental staff@ or subject-area consultants with relevant experience@ should be able to complete and document the evaluation process presented in this primer in less than one work week@ even for complicated sites with documented soil/groundwater impacts. For sites where impacts are localized and limited to surface/subsurface soils@ the analysis should require less than one work week. This document does not address petroleum ""spills"" that may require immediate@ emergency response activities."