This paper outlines the design of a comprehensive 3-dimensional ground water fate and transport model for US EPA risk assessments of a major federal facility. This fate and transport modeling and risk assessment effort has saved the U.S. taxpayer $250M in remediation costs. The model estimates the concentrations of key constituents at human receptors to evaluate the human health risks associated with site wide remedial designs of various operable units (OUs). This model accounts for the infiltration and mixing of contaminated surface runoff in a seasonal stream and subsequent infiltration into the regional aquifer, transport through an unsaturated glacial till and aquifer zones, movement of contaminants released by perched water and residual (remediated) areas, and transport through the saturated zone. The model identifies the OUs that contribute the greatest risk to a receptor, directs data collection and analysis efforts for other OUs, and establishes preliminary remediation goals (PRGs) and waste acceptance criteria (WACs) for various engineered barriers. The associated carcinogenic and noncarcinogenic risks to human health at the 10-6 incremental lifetime cancer risk determine these PRGs and WACs.