The National Center for Environmental Assessment (NCEA) has prepared this methodology in response to the 1993 Combustion Strategy for Hazardous Waste Incinerators released by the Administrator of the U.S. Environmental Protection Agency (EPA). Among other mandates regarding the regulation of this industrial sector, the strategy involved the requirement of EPA, or the regulated community, or both to conduct indirect exposure assessments to evaluate the impact of stack emissions. Although this mandate was specific to hazardous waste incinerators, the importance of the indirect pathways has extended to all combustors. The available methodologies at that time to conduct an indirect risk assessment were a 1990 document titled, 'Methodology for Assessing Health Risks Associated with Indirect Exposure to Combustor Emissions' (IEM) and the 1992 NCEA dioxin exposure reassessment to the Administrator's strategy, a workgroup composed of Office of Research and Development (ORD), Office of Solid Waste and Emergency Response (OSWER), Office of Air Quality Planning and Standards (OAQPS) and others, convened. The result of this workgroup was an 'Addendum' document to the 1990 Indirect Exposure document released in November of 1993. This 1993 document described updates and other changes to the 1990 document; these two documents, together with other relevant information such as that from the dioxin exposure document and the Exposure Factors Handbook, provided guidance on conducting indirect risk assessments. The Purpose of this document is to update the 1990 IEM. Most of the revisions provided in this document are based on EPA's Science Advisory Board (SAB) and Public comments to the 1993 Addendum. Earlier versions of this document have undergone internal Agency and external peer review.