Carbon Tetrachloride and Chloroform
Carbon tetrachloride contamination was found in
the unconfined aquifer beneath much of the
200-West Area. The contamination is believed to
be from waste disposal operations associated with
the Plutonium Finishing Plant. Carbon tetrachloride
was used as the carrier solvent for tributyl
phosphate in the final purification of weapons-grade
plutonium. Carbon tetrachloride was also used in
the same facility as a nonflammable thinning agent
in association with lard oil for machining of
plutonium. Carbon tetrachloride is immiscible in
water but exhibits a relatively high solubility
(
at 
). Carbon tetrachloride has
been found to have a relatively high degree of
mobility in ground water. Mobilization above the
water table can also occur through vapor transport.
A concentration of 
was found in a well
near the Plutonium finishing Plant first monitored in
October 1988 (well 299-W15-16). Carbon
tetrachloride concentrations in well 299-W15-16
remained fairly constant in 1994, reaching a
maximum of . Other wells in the
vicinity of the Plutonium Finishing Plant had
carbon tetrachloride levels ranging from 1,000 to
. The distribution of carbon
tetrachloride in the 200-West Area greater than the
Drinking Water Standard is shown in Figure 5.8.36.
The carbon tetrachloride distribution in the
200-West Area ground water has remained
relatively stable since the presence of the
contaminant plume was first noted in 1987. Figure
5.8.36 shows the trends in carbon tetrachloride
concentrations with time for wells located at the
east, west, north, and south parts of the plume. Well
699-39-79 shows a major increase during 1987 and
1988, indicating arrival of the bulk of the plume at
that time. Since 1988, the concentration in well
699-39-79 has remained relatively constant or
decreased slightly. Wells 299-W7-4 and 299-W6-2
in the north show an increase in concentrations in
recent years, although the most recent measurement
in 299-W6-2 is low. Concentrations in well
299-W18-21 exhibit increased concentrations of
carbon tetrachloride since approximately 1992, and
values continue to climb. Concentrations in wells
299-W19-16 to the southeast of the Plutonium
Finishing Plant have risen in recent years, while
well 699-38-70 exhibits fairly steady
concentrations.
The extent of carbon tetrachloride contamination is
poorly defined in several directions. The greatest
uncertainty lies in the extent of contamination to the
west and the northeast. In addition, there is
considerable uncertainty regarding the extent of
contamination in deeper parts of the aquifer.
Changes in ground-water flow since
decommissioning U Pond may influence the exact
plume configuration and the concentrations at
particular locations. Another potential influence is
the continued spreading of carbon tetrachloride
above the water table, in either the liquid or vapor
phase. Free-phase liquid carbon tetrachloride above
and possibly below the water table provides a
continuing source of contamination. Thus,
expansion of the carbon tetrachloride plume is
expected to continue slowly.
The Drinking Water Standard for carbon
tetrachloride is 
. In addition to carbon
tetrachloride, significant amounts of other
chlorinated hydrocarbon solvents were found in
200-West Area ground water, including chloroform.
The highest level recorded in 1994 was 
in one sample from well 299-W18-4. Well
299-W18-2, which contained the highest
concentrations of chloroform in 1993 samples, was
not sampled by the CERCLA Program in 1994.
The chloroform plume appears to be associated
with, but not exactly coincident with, the carbon
tetrachloride plume. The Drinking Water Standard
for chloroform is (total trihalomethanes),
20 times higher than that for carbon tetrachloride.
The location of the chloroform plume is shown on
Figure 5.8.37. Chloroform may result from the
degradation of carbon tetrachloride, either in the
process or in the subsurface, as the result of
biodegradation. The extent of chloroform
contamination appears to be decreasing
Trichloroethylene
Trichloroethylene has a Drinking Water Standard of
. In 1994, trichloroethylene was detected at
levels greater than the Drinking Water Standard in
wells in the 100-F, 100-K, 200-West, 300, and parts
of the 600 Area.
Trichloroethylene in the 100 Areas.
Trichloroethylene was detected in 1994 at levels
less than the Drinking Water Standard in 100-B/C
Area wells. It was detected at levels greater than
the Drinking Water Standard in 100-F Area wells.
The maximum concentration detected in the 100-F
Area in 1994 was 
in a sample for well
199-F7-1. In addition, trichloroethylene was found
at in well 699-77-36, west of the 100-F
Area, indicating a potential source upgradient.
Only one well sampled in 1994 in the 100-K Area
contained trichloroethylene at levels above the
Drinking Water Standard. However, other wells
sampled in previous years had reported
concentrations above the Drinking Water Standard
for at least one sample event. The maximum
concentration detected in 1994 was in
monitoring well 199-K-33.
Trichloroethylene in the 200 Areas.
Trichloroethylene was detected in 1994 at levels
greater than the Drinking Water Standard in the
200-West Area in several areas (Figure 5.8.38).
The first location is to the west of T Plant, and
concentrations up to were detected in
1994. The second location is near the U Plant.
Although only a few wells in this area contained
trichloroethylene at levels above the Drinking Water
Standard, the plume extends into the 600 Area to
the east, and the downgradient spread has not been
well-defined. Trichloroethylene contamination is
found near the Plutonium Finishing Plant, near the
source area for the carbon tetrachloride plume.
Trichloroethylene was also measured at in
a sample from well 299-W22-20 near the REDOX
Plant.
Trichloroethylene in the 300 Area.
Trichloroethylene was detected in several wells
throughout the 300 Area although levels were
generally below the Drinking Water Standard. The
highest level detected in the northern half of the 300
Area was 
in well 399-1-16B. This well
monitors the lower portion of the unconfined
aquifer system. Samples from this well also
contained up to of
cis-1,2-dichloroethylene, which is commonly found
as a biodegradation product of trichloroethylene.
The Drinking Water Standards for trichloroethylene
and cis-1,2-dichloroethylene are .
Trichloroethylene was also detected at levels above
the Drinking Water Standard in a few wells in the
southern half of the 300 Area. The maximum
concentration reported in 1994 was in
well 399-3-12.
Trichloroethylene in the 600 Area. Several wells
at the Solid Waste Landfill (part of the central
landfill) contained trichloroethylene levels less than
the Drinking Water Standard (maximum of
in well 699-23-34A). Solid Waste
Landfill wells had shown trichloroethylene
concentrations greater than the Drinking Water
Standard in previous years. The source of the
trichloroethylene in this area is apparently disposal
of waste from vehicle maintenance operations in the
mid-1980s through 1987. A sample from one well
south of Gable Mountain, 699-54-45A, contained
of trichloroethylene in 1994.
Trichloroethylene is found at levels above the
Drinking Water Standard in a number of wells in
the vicinity of Horn Rapids Landfill in the southern
part of the Site. This contamination forms a plume
leading towards the 300 Area but appears to have an
origin off the Hanford Site. The maximum
trichloroethyene contamination detected in this
plume in 1994 was in well 699-S31-E10A.
DOE monitors this plume under the 1100-EM-1
Record of Decision and through the Environmental
Surveillance Program. The Environmental
Surveillance Program also monitors the plume
through analyzing for concentrations of
trichloroethylene in soil gas above the plume. This
provides a cost-effective way to obtain further detail
on contaminant distribution.
Tetrachloroethylene
Tetrachloroethylene, also referred to as
perchloroethylene, was detected at low levels in a
number of areas of the Site including the 200-West
Area, the 300 Area, and parts of the 600 Area. A
number of samples from wells in the 1100 and
North Richland Areas contained low concentrations
of tetrachloroethylene. In 1994, tetrachloroethylene
was not detected at concentrations greater than the
Drinking Water Standard of in the Solid
Waste Landfill, where the concentrations reached a
maximum of in well 699-24-34C. In past
years, tetrachloroethylene has exceeded the
Drinking Water Standard near the Solid Waste
Landfill. Tetrachloroethylene is commonly used as
a degreasing solvent.
Radiological and Chemical Monitoring
Results for the Confined Aquifer
The uppermost (Rattlesnake Ridge) confined
aquifer was monitored to determine the extent of
ground-water contamination resulting from
interaction between the confined and unconfined
aquifers. Intercommunication between aquifers has
been previously identified by Gephart et al. (1979)
and Graham et al. (1984). Ground-water samples
from selected confined aquifer wells have been
analyzed for a variety of radionuclides and
hazardous chemicals. In most cases, no indication
of contamination was observed. Detection of
radionuclides in well 299-E33-12 is attributed to
contamination by high-salt waste that migrated by
density flow into the borehole when it was open to
both the unconfined and the confined aquifer during
drilling (Graham et al. 1984). The 1994 samples
from well 299-E33-12 contained up to 770 pCi/L of
tritium, similar to levels detected since 1991. The
1994 samples from this well also contain cobalt-60
at levels up to 36.4 pCi/L, nitrate at levels up to 46
mg/L, technetium-99 at levels up to 1530 pCi/L,
and cyanide at levels up to 
. Although all
of these are indicators of contamination, only nitrate
and technetium-99 were detected at levels greater
than the Drinking Water Standard.
Elevated levels of tritium have been measured in
ground water from the Rattlesnake Ridge interbed
in well 699-42-40C located adjacent to B Pond.
This well contained a maximum of 7,050 pCi/L of
tritium in 1994 samples, which were slightly lower
levels than in 1993, and well below the Drinking
Water Standard.
Samples collected in 1994 from well 199-B3-2P in
the 100-B Area, contained up to 20.9 pCi/L of
strontium-90 and 504 pCi/L of tritium. This well is
currently completed in the confined aquifer but was
open to both the unconfined and confined aquifer
between 1953 and 1970 so it is possible that the
well provided a conduit downward for
contamination in the unconfined aquifer. The
current extent of contamination in the confined
aquifer is unknown.
Figure 5.8.36
Figure 5.8.37
Figure 5.8.38
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