Encapsulation, one of the most commonly used abatement techniques for contamination in buildings, involves painting the contaminated surfaces with a coating material or sealant that serves as a barrier to prevent the release of a contaminant from the source, thereby improving the environmental quality in the building. The practice of encapsulating polychlorinated biphenyl (PCB)-contaminated surfaces began in the early 1970s and is still being used today. Although different levels of protective effects have been reported, a number of questions remain regarding this mitigation method, including: • To what extent can encapsulants provide protection from PCB contamination in buildings? • How long does the protective effect last? • What are the key attributes of a good encapsulant for PCBs? • What are the key factors that affect the performance of the encapsulants? • What are the limitations of the encapsulation method? This study addresses some of these questions and the results should be useful to mitigation engineers, building owners and managers, decision-makers, researchers, and the general public. E.2 Objective This study sought to develop a basic understanding of the encapsulation method for reducing PCB concentrations in indoor air and contaminated surface materials and of the behavior of encapsulated sources. The objectives of this study were to: • Select and develop experimental methods to evaluate the abilities of selected coating materials to encapsulate PCBs, • Identify useful tools for studying the behavior of encapsulated sources and predicting the performances of PCB encapsulants, • Determine the key factors that affect the performance of the encapsulants, and • Evaluate the effectiveness and limitations of the encapsulation method for reducing PCB concentrations in indoor air and contaminated surface materials.