The primary driving force behind investigating, evaluating, and, if necessary, remediating soils and groundwater is to manage risk to human health and the environment. Thus, the environmental community is accustomed to considering a variety of risk issues when assessing sites and selecting remedial alternatives. We frequently encounter a wide range of cleanup goals for the same chemical species even when the site geology and distribution of the chemical of concern are similar. In selecting remedial alternatives for a specific site, we require a sound basis for anticipating that the selected technology will meet the site-specific cleanup criteria. Because of the complex nature of the behavior of subsurface environments, there is always some risk inherent in the selection process. The level of risk associated with MNA is considered by some to be inherently greater than the risk associated with other technologies. This is based on the view that we do not thoroughly understand subsurface processes and we are not taking active steps to control or modify that environment. In fact, active remedies are also inherently risky because they may not work as intended, cause further spreading of the constituents of concern, or result in other unintended consequences. Typically, we manage these risks by conducting pilot studies and by monitoring the subsurface while conducting the pilot test and full-scale remediation.