1 - paducah environmental information center

Annual Site Environmental Report for 1999
4.1 Northeast Plume
4.1.1 Trichloroethene
Within the Northeast Plume, contaminant
levels above 5 Ilg!L cover a large area as a result
of several potential source areas. The highest
concentrations (as high as 1500 IlgIL in MW294)
are found ina-narrow core along the eastern edge
of the plume. The most upgradient source area
for this high concentration area appears to be
near the northwest comer of the C-333 Process
Building. An additional source area contributing
to the high concentration area appears to be in
the vicinity of the G· 340 Metals Reduction
Facility (1400 IlgIL detected). Neve':1heless,the
source to themairi plume centroid . of the
Northeast Plume remains undefined. Other areas
that appear to be contributing to the Northeast
Plume include the northeast comer of the C-400
Building and the C-410 Building. TCE
concentrations of 1700 IlgIL were measured
immediately northeast of the C-400 Building
during the WAG 6 investigation (DOE 1999a).
Further east, samples collected from MW260
have indicated TCE concentrations above 900
Ilg/L, interpreted to be sourced from the
northeast comer of the C-400 BUilding.
Of particular note, TCE concentrations
in some of the monitoring wells associated with
the main high concentration area near and within
the plant boundaries have shown a significant
decline in TCE concentrations. In 1995, samples
from MW258, immediately east of the C-755
Subcontractor Staging Area, had initial TCE
concentrations above 2300 IlgIL. The most
recent samples (11199) collected from this well
contained only 1100 - IlglL. This trend of
declining TCE levels suggests the DNAPL
source zone maybe rapidly depleting.
4.1.2 Technetium-99
Contaminant levels are generally less
than 25 pCilLoff-site and are only greater than
100 pCiIL at a few discrete sources. 'The most
upgradient source area appears to be the
northwest comer of the C-333 Process Building.
Lesser source areas downgradient of C-333 are
the C-340 Building (27 to 382 pCiIL detected)
and a classified materials storage area located on
the foundation of the former Kellogg Building!
SWMU 99 (137 pCilL detected). Increasing 99Tc
activity in monitoring well MW256 is indicative
of the Kellogg Building area source and
portends an off-site level greater than 25 pCiIL in
a discrete area of the Northeast Plume if remedial
actions. are not initiated.
Both the northeast comer of the C-400
Building and the C-410 Building appear to be
source areas of discrete centroids of
contamination moving to the east within the
broad boundaries of the Northeast Plume.
Technetium-99 activity is greater than 900 pCiI
L in the upper RGA beneath the northeast comer
of the C-400 BUIlding and interpreted to be
greater than 100 pCiIL beneath the C-4 to
Building.
4.2 Northwest Plume
4.2.1 Trichloroethene
Compared to the Northeast Plume, TCE
contamination in the Northwest Plume covers a
smaller geographic area. However, the TCE
concentrations in the core of the Northwest
Plume are higher than the TCE concentrations in
the Northeast Plume: Outside the security fence,
TCE concentrations measured in the core of the
Northwest Plume during 1999 were as high as
91 OOllgIL . (MW248), as compared to the
maximum concentration seen in the Northeast
Plume, 1500 Ilg'L Immediately downgradient
of the north extraction well field, measured TCE
concentrations during 1999 were as high as
1500 IlgIL ~MW236).
A possible TCE source area upgradient
of the C-400 Building was identified in the
vicinity of the C310 Product Building during the
WAG 28 RI (DOE 2000a). Alternate
interpretations of this area are possible which
may include the TCE being associated with
either the Northeast Plume or Southwest Plume
Appendix 0
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