Surface impoundments are used to treat, store, and dispose of waste water generated by facilities in many different industries. The Surface Impoundment Modeling System (SIMS) is a personal computer based program designed to estimate the air emissions from surface impoundments. The emission estimates are based on mass transfer models developed by the Emissions Standards Division (ESD) of the Environmental Protection Agency (EPA) during the evaluation of hazardous waste treatment, storage, and disposal facilities (TSDF's). SIMS allows the user to specify all required inputs to these emission models when the information is available, or when only limited information is available, provides default values for most of the model inputs. The manual presents a complete reference for all of the features and commands in SIMS.