Guidance for Conducting Risk Assessments and Related Risk ...

waterways that may have been contaminated by releases from the DOE-ORO installations. In 1989, the
ORR was evaluated by the EPA using the Hazard Ranking System. As a result of this evaluation, the
ORR was placed on the National Priorities List (NPL) and was required to comply with the requirements
of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) (DOE
1998b).
The ORR strategy for environmental restoration is to accelerate the transition from characterization
to remediation by making decisions at the watershed level based on assumed end uses (also referred to as
land uses) and existing/historical data. Until recently, the strategy for cleaning up ORR contaminated
sites was to investigate each area individually, identify chemicals of concern (and their potential human
health and ecological risks) for each site, and assume that the future land use of all sites on the ORR
would be unrestricted (e.g., residential, gardening, recreational, etc). The disadvantages of this site-bysite
approach are that it is time consuming, not cost-effective, and actions at one site could negatively
impact other nearby areas.
The ORR has adopted a new cleanup strategy called “The Watershed Approach”. This new strategy
involves making cleanup decisions for an entire watershed (a term used to describe a specific area where
surface water and often groundwater comprise a specific flow system). Because there are multiple
contaminated media and areas within a watershed, this new strategy’s cleanup actions rely heavily on the
massive amounts of existing/historical and current sampling data. The future land use for a particular
watershed (or area within the watershed) will be more accurately and realistically determined by the
DOE-ORO, the Tennessee Department of Environment and Conservation (TDEC), the U.S.
Environmental Protection Agency (EPA) Region IV, and the public. Cleanup criteria will be based on the
recommended future land use.
The watershed cleanup strategy uses a combination of integration point assessments, screening risk
assessments, and baseline risk assessments to:
• identify and prioritize contaminated sites and facilities within a watershed,
• determine local area end/land use (relying heavily on existing/historical environmental data), and
• develop an optimum remediation strategy (a remedy) for the identified problems.
Portsmouth Gaseous Diffusion Plant: The Portsmouth Gaseous Diffusion Plant was constructed in
the early 1950s to enrich uranium in support of both government and private programs. The plant
currently operates under a lease agreement with the U.S. Enrichment Corporation, which produces lowenriched
uranium for commercial applications. The DOE is responsible for remedial action to address
environmental releases and for decontamination and decommissioning (D&D) of the facilities.
The Portsmouth Gaseous Diffusion Plant is divided into four clean up areas, commonly referred to as
quadrants, based on groundwater flow direction. Remediation is accomplished for the quadrants by:
• removing well-defined sources of contamination,
• consolidating and integrating CERCLA-based remedial actions with Resource Conservation and
Recovery Act (RCRA) corrective measures and closures for individual or groups of Solid Waste
Management Units with common sources or interrelated groundwater plumes,
• using risk-based closure criteria rather than “clean closure criteria” (where practical), and
• establishing cleanup levels and the sequence of cleanup efforts based on risk analysis results.
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