Municipal wastewater treatment plants treat a wide variety of materials originating in the home including detergents, personal care products, and drugs and their metabolites. Environmental risk assessments for these materials include both fate and effects assessments. The fate assessment predicts environment concentrations typically through a series of mathematical models. Depending on the availability of data, assumptions are needed to parameterize these models. To avoid the extreme conservatism resulting from use of multiple conservative assumptions for model input parameters, uncertainty analysis was used to predict distributions for the parameters of interest (i.e., surface water concentrations). Variability predicted in model output more closely resembled environmental data than results of the conventional approach. For effects data, single species acute and chronic toxicity data can be used to construct effects distributions. The risk assessment is defined by the degree of overlap of the fate and effects distributions. C12LAS disposal into surface (i.e., riverine) waters is used as a case study to demonstrate this risk assessment process. The final C12LAS risk assessment demonstrates a low risk to environmental organisms of effects due to C12LAS exposure in riverine systems in the United States.