Ecological Risks of Environmental Restoration

Ecological risks of environmental restoration and waste management activities were evaluated as part of the project of preparing a Programmatic Environmental Impact Statement (PEIS) for DOE sites. Major issues for restoration include current contamination, residual contamination following remedial action, and adverse ecological impacts of remediation and new facility construction. For waste management, the ecological issues evaluated include (1) deposition of atmospheric contaminants on soil and (2) potential spills of radioactive, hazardous, and mixed waste during transport to central storage and disposal sites. The ecological risk assessment team included staff of ORNL's Environmental Sciences Division (ESD) and Advanced Sciences, Inc. Participating ESD staff members included Linda Mann, Lorene Sigal, Jerry Eddelmon, and Dan Jones.

The environmental restoration assessment focused on reservation-wide ecological resources. Of the approximately 30 facilities discussed in the impact statement, 6 were singled out for detailed ecological risk assessments: the Idaho National Engineering Laboratory, the Hanford Reservation, the Fernald Environmental Management Project, the Oak Ridge Reservation, the Portsmouth Gaseous Diffusion Plant.

To compare impacts among sites, the specific ecological resources on the six reservations were grouped into six categories:

Ecological resources falling into each of the six categories are identified from documents, maps, and contacts with resource management personnel on each reservation. The distribution of each resource on and near the facilities was mapped. These resource distributions were overlaid on the distributions of environmental restoration activities at each facility.

For contaminant exposures, transport media were identified and exposures were quantified using the same data sources and models employed in the human health risk assessments. The area disturbed by remedial action or construction activity was estimated, including both the actual contamination site and the surrounding area expected to be disturbed by road construction, dust, erosion, or noise. Ecological benefits and risks of remedial actions were evaluated by determining whether existing contamination poses a risk to ecological resources, evaluating the reduction in contaminant risk expected from remedial activities, and estimating the fraction of existing ecological resources that would be disturbed by restoration activities An example of such a disturbance would be loss of habitat for small mammals and birds from excavation of large volumes of contaminated soil.

For waste management (WM), the long-term accumulation of atmospheric contaminants emitted from waste treatment facilities was identified by DOE as a potentially significant ecological issue. These impacts were addressed using the Human Health WM team's atmospheric transport modeling results to estimate deposition and accumulation of radionuclides and toxic chemicals for different WM scenarios. The ecological exposure and effects models developed for the ER ecological risk assessment were then used to determine whether this accumulation could potentially affect plants or small mammals downwind from the facilities.

A "consequence assessment" was performed to evaluate the potential ecological risks of accidents involving radionuclide releases. A consequence assessment involves estimation of the ecological effects of a given size and type of accident but does not include estimation of probabilities of occurrence of accidents. Estimates of maximum credible radiological releases were obtained from Argonne National Laboratory for transportation accidents involving high-level waste, low-level waste, contact-handled transuranic waste (TRUW), and remotely handled TRUW shipments.

The scenario evaluated for the ecological risk assessment involves an accident in which the contents of a rail shipment are spilled into a stream. Assessments were performed for five stream size classes ranging from a small, second-order stream with a flow rate of a few cubic meters per second to a major continental river such as the Mississippi River.

Two alternative assumptions were made about the fate of the spilled material. First, it was assumed that all material remains suspended or dissolved in the water column and is transported downstream. For this scenario, the team estimated (1) the length of stream (m) of each size class that would be affected before longitudinal dispersion reduced the dose rate below the safe level (1 rad/day) recommended by the National Council on Radiation Protection for protection of aquatic life and (2) the time required (h) for this dispersion to occur.

Alternatively, it was assumed that all of the spilled material is immediately deposited on the bottom of the stream at the site of release, where it becomes incorporated in bottom sediment. Biota present at the release site receive radiation exposure over their whole lifetime and can receive both external and internal doses. For this scenario, the team estimated the total number of kilograms of clean sediment required to dilute the spilled material to a sediment activity level corresponding to a 1 rad/day lifetime dose to a large fish residing at the bottom of the stream and feeding on benthic biota. This quantity should be a reasonable estimate of maximum mass of sediment that would have to be removed during a remedial action taken following the spill. The final comparison evaluated the maximum ecological consequence of potential spills for each waste type.

Results of the waste management assessment showed that the physical form of the transported waste is much more important than either the total radiological activity or the size of the shipment in determining the potential ecological consequences of a spill. It now appears that the results of the ER ecological risk assessment will not appear in the PEIS because of scope changes that occurred after most of the work was completed. However, the reservation-wide approach adopted for the PEIS fits well into DOE's new policy of including future land use as a key factor in setting environmental restoration goals for its facilities, land use, and stewardship of its lands. We hope that the results of our assessment will support DOE in implementing this policy. --Larry Barnthouse

Biographical Sketch

Larry Barnthouse is a senior research staff member in ORNL's Environmental Sciences Division. He has an A.B. degree in biology from Kenyon College and a Ph.D. degree in biology from the University of Chicago. He has been on the staff of the Environmental Sciences Division since 1976. Since that time he has been involved in dozens of environmental research and assessment projects involving development of new methods for predicting and measuring environmental risks of energy technologies. Barnthouse has been the author or co-author of nearly 100 publications relating to ecological risk assessment. He has received two Martin Marietta Energy Systems Technical Achievement Awards and was named Energy Systems Author of the Year for 1991.

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