Report on the remedial investigation of Bear Creek Valley at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee. Volume 6: Appendix G -- Baseline ecological risk assessment report Page: 81 of 882
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G2-17
G.2.3.6 Weight of Evidence for Fish
Current risks
The weight of evidence suggests that water from Bear Creek and tributaries NT-2 through NT-8
does not pose a significant risk to the fish community or the Tennessee dace. Table G.10 summarizes,
for each site, the weighing of evidence presented in the following text.
The fish community in Reach 1 does not appear to be significantly degraded relative to reference
streams. Species richness and total density of the fish community has increased since 1989 and is
comparable to reference communities. Survival and reproduction of C. dubia are still drastically reduced
relative to controls. Calcium and manganese concentrations were significantly correlated with these
responses. Dietary exposures to mercury and PCBs do not appear to be toxic, based on the body burden
measurements of these chemicals. Calcium, cadmium, and uranium concentrations are likely to be toxic.
Also, nickel is likely to be toxic to sensitive species. Toxicity is possible, but not likely, from barium and
copper. Although the toxicity tests and media analyses were positive, a community-level effect was not
evident. This suggests that the BCV fish community is less sensitive than the surrogate test organisms
to the elevated chemical concentrations present in Bear Creek. This could be due to inherent differences
between species and/or acclimation of the Bear Creek community to existing conditions.
The fish communities in Reaches 2, 3, and 4 also do not appear to be degraded by a contaminant
effect. Species richness and densities were generally comparable to reference streams. The lower
densities observed at some sites (e.g., BCK 11.09 and BCK 7.87) appear to be attributable to poor
habitat quality, including low stream flow and siltation from construction activities. The toxicity tests
are not indicative of significant current effects, and the chemical analyses suggest that the likelihood of
toxicity decreases with increasing distance from Reach 1. Hence, water in these reaches appears to pose
less of a risk to fish than does water in Reach 1. The body burden measurements are the only line of
evidence that suggests risk increases with increasing distance from Reach 1. Significant toxicity is not
expected in Reach 3, given that mercury concentrations are below all benchmarks and PCB
concentrations exceeded only one very low screening value. Measured mercury and PCB concentrations
in rock bass fillets from Reach 4 (BCK 0.7) suggest that toxicity to sensitive species is possible, but
unlikely. However, increasing mercury concentrations suggest that risks may increase in the future. The
cause of this increase is unknown, but a similar phenomenon is occurring in EFPC.
Water from tributary NT-2 does not appear to pose a significant risk to fish inhabiting this area.
Only two lines of evidence are available: aqueous toxicity tests and aqueous chemical concentrations.
C. dubia reproduction was reduced by 37% in one of two tests, though survival was 100% in both tests.
Calcium concentrations were significantly correlated with this response. Fathead minnows were not
significantly affected. Toxicity is likely from calcium and possible, but not likely, from barium.
Community surveys were not conducted for the tributaries. However, Reach 1 water was more toxic
(i.e., higher intensity and frequency of effects) and more contaminated (i.e., more COPECs at higher
concentrations) than NT-2. Given that the fish community in Reach 1 is not at risk, it is highly unlikely
that the fish using NT-2 are at risk. Also, the fish in NT-2 are functionally part of the community in
Reach 1, because NT-2 is too small to support a distinct fish community.
Water from tributaries NT-3 through NT-8 also do not appear to pose a significant risk to fish
inhabiting these area. Only two lines of evidence are available: aqueous toxicity tests and aqueous
chemical concentrations. C. dubia and fathead minnows were not significantly affected during the two
tests conducted using water from these sites, and none of the COPECs occurred at concentrations likely
to be toxic.
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Report on the remedial investigation of Bear Creek Valley at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee. Volume 6: Appendix G -- Baseline ecological risk assessment report, report, September 1, 1996; United States. (https://digital.library.unt.edu/ark:/67531/metadc675908/m1/81/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.