Liquid effluent monitoring for research and development laboratories is difficult because of the diverse and variable effluent streams and wide range of chemicals used in continuously changing projects. Risk assessment tools can aid in the design of reasonable monitoring programs. In this paper, an assessment was performed to determine the human health risk of accidental discharges of chemicals into the sewer systems servicing research and development laboratories at the Hanford Site's 300 Area. As part of this assessment, the single largest container of chemical compounds used in the laboratories was assumed to be discharged into the sewer system transported to a treatment facility, then pass untreated into the Columbia River. The Multimedia Environmental Pollutant Assessment System was used to model the transport and fate of the chemical contaminants, and exposure estimates were obtained for two receptor locations and for population impacts. Results of this assessment indicated that the human health risk from the source terms analyzed would not exceed levels generally accepted as safe and that no additional controls or monitoring of specific chemicals were indicated from this risk perspective.