The Army Corps has divided the NFSS into three OUs to help to organize its decision-making regarding possible remediation by addressing contamination in a logical order. Decisions made in each of the earlier OUs affect the scope and potential actions of subsequent OUs. Each of these three OUs will have their own remedial investigation and feasibility study process.

Interim Waste Containment Structure (IWCS) OU

The IWCS OU is defined as waste material (i.e., residues and other remedial action waste) that the Department of Energy (DOE) placed in the IWCS. The scope for the IWCS OU involves development of remedial alternatives for addressing the residues and other waste material only. If all of the waste materials in the IWCS are removed, then the remaining IWCS structure (e.g., remaining cap material, the dike, cut-off walls, residual soil that had waste placed on them, etc.) would be addressed within the scope of the BOP OU, as described below. For any alternatives that involve leaving any waste materials in the IWCS, the FS would have to demonstrate that the alternative is protective of human health and the environment, including surface waters and the groundwater system beneath the IWCS.

STATUS: The IWCS Feasibility Study is underway. The Corps is releasing a series of five technical memoranda to help the public understand key issues and provide input as the process moves forward. The last of the technical memoranda will be released summer 2013 with the full FS report expeced in 2014 and final decision in 2015.

Balance of Plant (BOP) OU

The BOP OU is defined as all material not included in the IWCS OU, excluding groundwater. BOP material will include any remaining former building structures within the IWCS, remaining cap material and other soils within the IWCS, the IWCS dike, surface and subsurface soils across the rest of the site, surface water, sediment, railroad ballast, roads, Building 401, and pipelines, etc. Additionally, only structures that need to be removed to obtain access to underlying contamination will be included in the BOP OU. For example, tank cradles may not be removed if they show no risk to human health and the environment from site contaminants, and their removal is otherwise deemed unnecessary. The remaining IWCS structures, subsurface soils and dike are only addressed in BOP alternatives if all of the residues and wastes placed in the IWCS are removed. The impacts, if any, of the BOP OU alternatives on groundwater and surface water will be addressed in the alternative evaluations for the BOP OU. 

STATUS: Field work is underway to gather additional information for the BOP project. The Feasibility Study and decision will follow the decision for the IWCS to coordinate with decisions made.

Groundwater OU

The Groundwater OU is defined as groundwater remaining in both the upper water-bearing zone (UWBZ) and the lower water-bearing zone (LWBZ) after implementation of the selected remedial actions for the IWCS and BOP OUs. As only the UWBZ has been impacted by site contaminants, groundwater contamination may be ultimately addressed by remediation of soils (e.g. by controlling/removing the sources of contaminant migration).


STATUS: Work on Groundwater will follow the other two operable units. The Feasibility Study and decision will follow the decision for the IWCS and BOP to coordinate with decisions made and ensure that appropriate groundwater cleanup and controls are in place.