The available data were gathered for a large number of case studies of hazardous waste surface impoundments (SI). Actual and projected performances were compared. This collection, analysis and dissemination of the accumulated experience can contribute significantly to improving SI design, construction and operation. Nine facilities were reviewed and assessed. They represent a range of industries, waste types and volumes, ages, environmental settings, liner types and designs, and systems for leak detection and groundwater monitoring. In addition, nine interviews were held with technical experts in four consulting engineering firms, one waste management company, one liner fabricator/installer, and regulatory agencies in three states. Based on case studies and professional opinions and experiences collected, recommendations for research and development are presented.