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

Annual Site Environmental Report
Fig. 4.32. Comparison of mean sensitive species richness (number of species)
collected each year from 1985 through 2008 from four sites in East Fork Poplar Creek
and a reference site (Brushy Fork).
Reality. However, the East Fork Poplar Creek fish community continues to lag behind reference stream
communities in most important metrics of fish diversity and community structure, especially at the
monitoring site closest to the Y-12 Complex.
4.6 Groundwater at the Y-12 Complex
Groundwater monitoring at Y-12 is performed to determine what impacts to the environment from
legacy and current operations are occurring. More than 200 sites have been identified at the Y-12
Complex that represent known or potential sources of contamination to the environment as a result of past
operational and waste management practices. Monitoring provides information on the nature and extent of
contamination of groundwater which is then used to determine what actions must be taken to protect the
worker, public, and the environment in compliance with regulations and DOE orders. Figure 4.33 depicts
the major facilities or areas for which groundwater monitoring was performed during CY 2009.
4.6.1 Hydrogeologic Setting
The Y-12 Complex is divided into three hydrogeologic regimes (i.e., Bear Creek, Upper East Fork
Poplar Creek, and Chestnut Ridge), which are delineated by surface water drainage patterns, topography,
and groundwater flow characteristics (Fig. 4.34). Most of the Bear Creek and Upper East Fork Poplar
Creek regimes are underlain by fractured noncarbonate rock. The southern portion of the two regimes is
underlain by the Maynardville Limestone, which is part of the Knox Aquifer. The entire Chestnut Ridge
regime is underlain by the Knox Aquifer. In general, groundwater flow in the water table interval follows
the topography. Shallow groundwater flow in the Bear Creek and the Upper East Fork regimes is
divergent from the topographic and groundwater divide located near the western end of the Y-12
Complex that defines the boundary between the two. In addition, flow converges on the primary surface
streams (Bear Creek and Upper East Fork Poplar Creek) from Pine Ridge and Chestnut Ridge. In the
Chestnut Ridge regime, a groundwater divide exists that approximately coincides with the crest of the
ridge. Shallow groundwater flow tends to be toward either flank of the ridge, with discharge primarily to
surface streams and springs located in Bethel Valley to the south and Bear Creek Valley to the north.
The Y-12 National Security Complex 4-59