"“Volume of Contaminated Medium Addressed” refers to:
The volume of environmental medium that is subject to the Superfund response action or RCRA corrective action, such that, at the conclusion of the action, human health and the environment are protected in accordance with the statutory mandate for Superfund or RCRA Corrective Action.
The focus is on the physical space that is addressed by the response or corrective action. As an example, for soil and groundwater remedies, the volume of medium measures the volume of soil or aquifer subject to the response or corrective action. In the case of soil contamination, the volume of contaminated medium is the volume of soil subject to removal or treatment. In the case of groundwater contamination, the volume of contaminated medium is the volume of physical aquifer (not water, but entire formation) that will be addressed by the response or corrective action. These are further elaborated in the sections that follow."
Source: 12/12/03 "Final Methodology for Estimating Superfund and RCRA Corrective Action Case Conclusion Data Sheet (CCDS) Environmental Benefits", p. 5 of the guidance.