1 - paducah environmental information center

Paducah Site
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downgradient well on the east side of the plume
(MW242) remain above 100 11g/L.
North Well Field
The monitoring well data for the north well
field suggest that, like the South Well Field, the
North Well Field is more effective in capturing
the west side of the plume than the east side. The
two downgradient wells on the east side of the
plume have shown steady increases in TCE
concentrations to over 1000 11g/L over the past
year and a half. For the last half of 1999, most of
the wells in the North Well Field have shown an
increase in TeE concentrations,suggesting the
possibility that a volume of groundwater
containing a higher concentration of TCE is
beginning to migrate through the area.
5.2.2 Technetium-99
South Well Field
Groundwater analyses for monitoring
wells of the South Well Field convincingly
demonstrate capture of the ~ 900 pCiIL plume
centroid. In general, the extraction well field is
apparently capturing the west side of the plume
(~ 25 pCiIL) although groundwater containing
several hundred pCiIL 99Tc is migrating past the
east side of the well field.
During December 1999, monitoring
wells MW-245 (on the west side of the well field)
and MW-248 (located between the two
extraction wells) experienced a sharp increase in
99Tc levels. Contaminant trends suggest these
detections are an aberration that will not be
repeated. However, it remains possible that CY
2000 analyses may suggest a significant shift of
the pillme centroid to the west. Groundwater
monitoring results will continue to be assessed to
evaluate shifts in the plume location.
North Well Field
Although less definitive, 99Tc analyses
for the North Well Field suggest that the
extraction wells (particularly EW 229) are
capturing the > 900 pCilL centroid. It appears
that both extraction wells, together, probably
capture the west side of the plume. Technetium-
99 activities of> 500 pCiIL continue to migrate
past the east side of the well field.
The analyses of 1999 reveal a slight
increase in Y9Tc activity on the west side of the
plume during the fourth quarter. Technetium-99
levels in monitoring wells on the east side of the
well field continue a trend begun in 1998 of
sharply increased acti vity.
6. USES OF THIS REPORT
This evaluation of groundwater
contaminant trends for CY 1999 supports
several goals of the PGDP environmental
program. Foremost, the updated plume maps
and definition of trends will be used in the
preparation of the Groundwater Operable Unit
Feasibility Study to provide the following
information:
• define additional areas contributing
significant contamination to the RGA,
• scope the dimensions of potential
remedial actions, and
• refine the extent of off-site areas that
will be addressed by temporary or
permanent institutional controls.
This same assessment will support the
ongoing evaluation of the adequacy of DOE's
Water Policy and effectiveness of the PGDP
groundwater monitoring program. To this end,
this report will be included as an appendix to the
1999 Annual Site Environmental Report. In
addition, the trends and extent of contamination
defined by this report will help identify areas of
groundwater/surface water interaction to be
considered in the upcoming RI of the Surface
Water Operable Unit.
Appendix D