This paper presents the results of a national scale evaluation of the environmental impact of surface impoundments that contain non-hazardous wastewaters. In the 1990s, it was found that approximately 18,000 surface impoundments existed in the US for treating, storing or disposing of non-hazardous wastewater. In this study, the focus was on the subset of 11,900 impoundments that contain at least one of 256 chemicals of interest or high or low pH wastewater. Questionnaires were sent to facilities chosen in a two-phase nationally representative random sample. The nature, extent and use of surface impoundments across manufacturing industries were characterized using the information collected in the survey. Also, the chemical composition of impounded wastewaters; the potential for chemical releases to the environment from the impoundments; and the risk from these releases were assessed. It is estimated that only approximately 5–6% of facilities with impoundments have the potential to pose risks to human health, although approximately 19–46% of facilities with impoundments release chemicals of concern to the environment. The information in this study should help environmental managers evaluate and avoid those risk factors that have the potential to result in environmental harm, particularly when present in combination.