DOE/ORO/2327 Oak Ridge Reservation Annual Site Environmental ...

Oak Ridge Reservation
Fig. 4.28. Locations of biological monitoring reference sites in relation to the Oak
Ridge Y-12 National Security Complex.
4.5.9.1 Bioaccumulation Studies
Mercury and PCB levels in fish from East Fork Poplar Creek (EFPC) have been historically elevated
relative to fish in uncontaminated reference streams. Fish in EFPC are monitored regularly for mercury
and PCBs to assess spatial and temporal trends in bioaccumulation associated with ongoing remedial
activities and Y-12 Complex operations.
As part of this monitoring effort, redbreast sunfish (Lepomis auritus) and rock bass (Ambloplites
rupestris) are collected twice a year from five sites throughout the length of EFPC and are analyzed for
tissue concentrations of mercury (twice yearly) and PCBs (annually). Mercury concentrations remained
much higher during 2009 in fish from East Fork Poplar Creek than in fish from reference streams.
Elevated mercury concentrations in fish from the upper reaches of EFPC indicate that the Y-12 Complex
remains a continuing source of mercury to fish in the stream. Although waterborne mercury
concentrations in the upper reaches of EFPC decreased substantially following the 2005 start-up of a
treatment system on a mercury-contaminated spring (Fig. 4.29), mercury concentrations in fish have not
yet decreased in response and were significantly higher in 2009 than in recent years. Mean concentrations
of PCBs in fish at EFK 23.4 (the site where PCBs in fish are highest) continued to be much lower in 2009
than peak concentrations observed in the mid 1990s (Fig. 4.30).
4.5.9.2 Benthic Invertebrate Surveys
Benthic macroinvertebrate communities were monitored at three sites in East Fork Poplar Creek and
at two reference streams in the spring of 2009. The macroinvertebrate communities at EFK 23.4 and
EFK 24.4 remained degraded as compared with reference communities, especially in the richness of
pollution-sensitive taxa (i.e., EPT taxa richness; Fig. 4.31). Of note is a similar recent trend of reductions
4-56 The Y-12 National Security Complex