The concept for a Web-Based Risk Assessment Modeling System was originally introduced during an U.S. Army Corps of Engineers Risk Assessment Modeling Workshop held in New Orleans, Louisiana, May 1998. The workshop included experts from across the country involved in the area of risk assessment modeling. The objective of the workshop was to conceptualize a procedure which could be utilized to develop a state-of-the-art modeling system to conduct risk assessments for both ecological and human endpoints. A key component for the system would be the requirement to address uncertainty involved in the modeling process. The uncertainty inherent in predicting ecological and human risk from contaminant uptake across spatial and temporal dimensions would have to be quantified. It was decided that the Army Risk Assessment Modeling System (ARAMS) would contain the following components: (1) screening level models, (2) comprehensive models, (3) population models, (4) an uncertainty component, (5) bioaccumulation databases, and (6) effects databases. ARAMS should allow the calculation of exposure concentrations in various media, the effects of the concentrations on human or ecological endpoints, and the associated risk while incorporating uncertainty. This paper describes in more detail the conceptual model constructed during the U.S. Army Corps of Engineers workshop.