LOW RESOLUTION SEDIMENT CORING REPORT

EXECUTIVE SUMMARY July 1998

This report presents the findings from the analysis of data relating to the low resolution
sediment coring program for the Hudson River PCBs Site Reassessment Study. The low
resolution sediment coring program was designed to evaluate changes in sediment PCB
inventory over time and the degree of burial of PCB-contaminated sediments.

Low resolution coring refers to the relative thickness of the sediment slices analyzed during
the sampling program. In the low resolution coring program, the average thickness of a
sediment slice was 9 inches (22 cm), compared to the 0.8-inch (2 cm) to 1.6-inch (4 cm)
slices analyzed in the high resolution coring program.

The Low Resolution Sediment Coring Report is a companion to the Data Evaluation and
Interpretation Report, which was issued in February 1997. Similar to the Data Evaluation
and Interpretation Report, the Low Resolution Sediment Coring Report is based on
geochemical analysis. However, whereas the Data Evaluation and Interpretation Report
primarily evaluated the transport of PCBs through the analysis of water-column data and
dated sediment cores, the Low Resolution Sediment Coring Report assesses the inventory of
PCBs found in the Upper Hudson River sediments. The geochemical analysis in these reports
will be complemented and verified to the extent possible by additional numerical analysis
(i.e., computer modeling). Results of the computer modeling will be reported in the Baseline
Modeling Report, to be released in May 1999. In addition, the Low Resolution Sediment
Coring Report does not explore the biological uptake and human health impacts, which will
be evaluated in future Reassessment documents.

The Reassessment Remedial Investigation and Feasibility Study is being conducted by the
U.S. Environmental Protection Agency in order to determine an appropriate course of action
to address the PCB-contaminated sediments in the Upper Hudson River. This study is a
reassessment of the Agency’s interim "no-action" decision made in 1984. During the first
phase of the Reassessment, EPA compiled existing data on the site and conducted
preliminary analyses of the data. As part of the second phase, EPA conducted field
investigations to characterize the nature and extent of PCB contamination in the Upper
Hudson. The Phase 2 data, along with data from other sources, has been used to better
understand the fate and transport of PCB contamination in the river.

Two large-scale sediment investigations were previously conducted by the New York State
Department of Environmental Conservation (NYSDEC) to characterize the extent and
magnitude of PCB contamination in the sediments--one from 1976 to 1978, and one in
1984. On the basis of data gained from these investigations, approximately forty zones of
highly contaminated sediments, designated as hot spots, were identified. These data were
used to estimate total PCB inventory in Hudson River sediments at the time of the completion
of both the 1976-1978 and 1984 studies.

Objectives - The low resolution sediment coring program, conducted in July and August
1994, had two main objectives:

• Obtain new estimates of sediment PCB inventories at selected
locations in the Thompson Island Pool to compare against the
existing PCB sediment database constructed from the 1984
NYSDEC survey; and

• Refine the PCB mass estimates for a limited number of historic
hot spot locations defined by the 1976-1978 NYSDEC survey in
the Upper Hudson below the Thompson Island Dam.

Low resolution sediment coring was performed to examine PCB contamination in a limited
number of areas and to augment and improve estimates of the sediment inventory and spatial
distribution of PCBs previously developed for these areas. The comparison of previous
surveys to current conditions is significant to the Hudson River PCBs Reassessment because
changes in PCB inventories can indicate areas of the river where PCBs are being lost and/or
gained.

In the Thompson Island Pool, locations for most of the cores were selected by grouping the
samples into zones with minimal local sediment heterogeneity, thereby minimizing uncertainties
due to factors other than PCB inventory changes. It was then possible to compare the 1994
data to the 1984 NYSDEC data and draw general conclusions regarding PCB inventory
change in the Thompson Island Pool. The coring locations below the Thompson Island Dam
were selected to generate PCB mass estimates for areas which, based on previous estimates,
represented approximately 75 percent of the hot spot inventory below the dam. While these
areas should be indicative of areas with similar levels of contamination (i.e., hot spots), the
results cannot be extrapolated to inventory changes in other areas below the Thompson
Island Dam. Other locations sampled were selected to characterize near-shore sediments.

Analytical Tools - Low resolution sediment core samples were analyzed on a
congener-specific basis for PCBs, which allows for the same type of analysis of
dechlorination products as was conducted for the Data Evaluation and Interpretation Report.
In addition, radionuclide analyses of the isotopes cesium-137 and beryllium-7 in sediments
were conducted. Beryllium-7 data were used to determine whether the top of the core
showed evidence of recent deposition. The cesium-137 data were used to establish that the
core had penetrated all post-1954 sediment, which correlates to the PCB-containing
sediments. The radionuclide data allowed the low resolution cores to be assessed for
completeness, because the absence of cesium-137 in the bottom of the core was a reliable
indicator that the core did not miss any PCBs at depth (i.e., the core was complete).
Because the 1994 inventories are from cores that were determined to be complete, and
because the previous inventories did not utilize radionuclide analyses and therefore may have
been underestimated, the observed losses in PCB inventory are minimum estimates.
Likewise, the observed gains in PCB inventories in certain areas are maximum estimates.

Major Findings - The analyses presented in the Low Resolution Sediment Coring Report
lead to four major findings as follows:

2. From 1984 to 1994, there has been a net loss of approximately 40 percent of the
PCB inventory from highly contaminated sediments in the Thompson Island Pool.

3. From 1976-1978 to 1994, between the Thompson Island Dam and the Federal
Dam at Troy, there has been a net loss of PCB inventory in hot spot sediments
sampled in the low resolution coring program.

These conclusions are briefly described and explained below:

1. There was little evidence found of widespread burial of PCB-contaminated
sediment by clean sediment in the Thompson Island Pool. Burial is seen at some
locations, but more core sites showed loss of PCB inventory than showed PCB gain
or burial. Thirty percent of coring sites do not exhibit burial, or may exhibit erosion, based
on the absence of beryllium-7 in core tops. Comparisons of sediment core profiles between
the 1984 and 1994 data indicate that burial is not occurring at more than half of the locations
investigated. Burial does occur at some hot spot areas, but there is also evidence of sediment
PCB loss occurring, often within the same hot spots. Again, there is more evidence for
sediment PCB loss rather than burial.

Beryllium-7 is a naturally-occurring isotope whose presence in sediments indicates recent
deposition or interaction with surface waters within the six months prior to sample collection.
The absence of beryllium-7 was shown to be a statistically significant indicator of inventory
loss. Absence of beryllium-7 is attributed to a core collected in a non-depositional area or an
area that has undergone scour (erosion) of river sediment. Thus, this radionuclide was used
to test a core top (0 to 1-inch) for the presence of recently deposited sediment. Surficial
sediments in which beryllium-7 was not detected (no burial) had lower PCB inventories than
cores in which beryllium-7 was detected, indicating that burial of PCB mass by less
contaminated sediments is not occurring at these locations. Although this analysis does not
offer proof of sediment scour, it does show that burial of contaminated sediments is not
occurring in at least 30 percent of the coring sites.

The core profiles, or core results presented by depth, show an important finding. PCB
maxima are principally found in the top-most core layer in approximately 60 percent of the
samples, which represent shallow sediment (median core segment depth of 9 inches). These
results indicate that burial of PCB-bearing sediments is not occurring on an extensive basis
and that high concentrations of PCBs remain relatively close to the sediment/water interface.
In addition, in areas where burial does occur, the newly deposited sediments commonly
contain PCBs.

In addition, the average depth to the maximum total-PCB concentration (taken as the bottom
of the core section in which the PCB maximum was found) varied considerably according to
whether the area showed a gain or loss of PCB inventory. In the hot spots, for cores
exhibiting a PCB inventory increase, the average depth to the maximum total-PCB
concentration was 18.7- inches (46.8-cm), contrasted to 10.6 inches (26.5-cm) in the cores
exhibiting a loss of PCB inventory. The difference in mean depth between areas of PCB loss
and gain is statistically significant. This finding confirms that the PCB-maximum moves
downward in areas of PCB (and accordingly, sediment) gain, and does not exhibit such
burial in areas where PCB loss is occurring.

2. From 1984 to 1994, there has been a net loss of approximately 40 percent of the
PCB inventory from highly contaminated sediments in the Thompson Island Pool.
Sediments in the Thompson Island Pool with total PCB inventories of greater than 10 g/m2
(typical of hot spot sediments) exhibit a statistically significant loss of PCBs. This inventory
loss includes loss to the overlying water column as well as dechlorination. Specifically, there
has been roughly a 30 percent decline in inventory due to actual loss from the sediments
(from erosion, diffusion, groundwater advection, or other mechanisms) and a 10 percent loss
via dechlorination. When the 30 percent loss is combined with an average dechlorination loss
of approximately 10 percent, the result is a total PCB inventory loss of approximately 40
percent.

The PCBs lost from hot spot areas enter the water column and may be available to the food
chain or deposited in other areas.

3. From 1976-1978 to 1994, between the Thompson Island Dam and the Federal
Dam at Troy, there has been a net loss of PCB inventory in hot spot sediments
sampled in the low resolution coring program. When the 1994 total PCB inventory is
compared to the 1976-1978 inventory, a statistically significant loss of 50 to 80 percent of
PCB inventory is seen for Hot Spots 31, 34 and 37. This represents a potential loss of
approximately 3 metric tons into the water column, although some loss may be due to
dechlorination. The other hot spots evaluated either appear unchanged or have not
experienced significant gains in PCB inventory, with the exception of Hot Spot 28 , as noted
in Major Finding 4, below.

Hot Spot 39 exhibits burial. Total PCB concentrations are at greater depths than previous
sediment surveys. Because of the inability to obtain "complete" cores in this hot spot, there is
uncertainty in our current estimate as well as the previous estimates, making it difficult to
determine whether there is inventory loss or gain. Given this uncertainty, Hot Spot 39 is
considered to not have experienced a significant change in inventory.

The sediment inventories of three other areas appear unchanged (Hot Spots 25, 35 and
dredge location 182), but only one (Hot Spot 25) had a sufficient number of samples to
confirm the lack of change.

It should be noted that the calculations for Hot Spots 28 and 39 show large PCB inventories
of 20 and 4 metric tons, respectively. This is greater than the inventory of the entire
Thompson Island Pool, which was estimated to be between 14.5 and 19.6 metric tons in the
Data Evaluation and Interpretation Report, based on the 1984 NYSDEC data.

Overall, hot spot sediments below the Thompson Island Dam exhibit both losses and gains
based on 1976-1978 and 1994 inventory estimates. Losses total a minimum of 3 metric tons.
Apparent gains in certain hot spots were likely due to previously inaccurate estimates.

4. The PCB inventory for Hot Spot 28 calculated from the low resolution coring data
is considerably greater than previous estimates. This apparent "gain" in inventory
is attributed to significant underestimates in previous studies rather than actual
deposition of PCBs in Hot Spot 28. An evaluation of the 1994 data collected for the low
resolution coring program found that the PCB inventory in Hot Spot 28 was substantially
greater than had been estimated in previous studies. The Low Resolution Sediment Coring
Report estimates the mass of PCBs in Hot Spot 28 to be 20 metric tons. Previous estimates
varied between two to seven metric tons. Therefore, based on a comparison of these
estimates there would appear to be a large gain in PCB inventory. However, further
examination of the core profiles for Hot Spot 28 shows that less than 50 percent of the
sample locations have evidence of deposition (burial). The remaining sites are either
unchanged or have undergone scour based on the presence of the maximum total-PCB
concentration in the shallow sediment. The deposition history recorded by the nearby high
resolution cores indicates that this type of profile can only be caused by scour. Only between
two to five percent of PCB mass was deposited between 1977 and 1991 for two nearby
high resolution cores, thus making such a large gain in inventory unlikely. Therefore, the
apparent "gain" of PCBs in Hot Spot 28 based on a comparison of historical estimates to the
current estimate is not real. There have been losses of PCBs from several locations within the
hot spot but, overall, the evidence suggests no significant change in inventory in the hot spot.
The previous mischaracterization of the inventory probably results from an initial inaccurate
assessment of Hot Spot 28 by the 1976-1978 sediment survey caused by too many shallow
cores and grabs (i.e., "incomplete" cores). EPA’s current estimate is based on cores that
have been found to be "complete" based on radionuclide analysis.

Additional Findings

The interpretation of the low resolution coring data is consistent with the findings of the Data
Evaluation and Interpretation Report. The analysis in the Low Resolution Sediment Coring
Report supports the conclusions from the Data Evaluation and Interpretation Report that the
extent of dechlorination is proportional to sediment concentration, and that the water-column
PCB load originates primarily from the sediments of the Upper Hudson River.

There has been a net gain of PCB inventory in areas of the Thompson Island Pool outside of
the hot spots. The additional PCBs may have come from redistribution of PCBs from high
concentration areas or from PCBs that entered the pool from upstream sources, such as the
GE Hudson Falls Plant site. Sediments with total PCB inventories of less than 10 g/m2 exhibit
a statistically significant gain of PCBs. However, this net gain is found at a limited number of
locations, insufficient to support such a finding for all non-cohesive (coarse-grained)
sediments in the Thompson Island Pool. The increase of PCB inventory in the Thompson
Island Pool outside of the hot spots has an upper bound of approximately 100 percent,
although the actual gain is probably much less.

Comparison of the river bottom texture type indicated by the side-scan sonar images with the
1976-1978 NYSDEC sediment survey grain-size data resulted in good agreement with one
another. This indicates that side-scan sonar can be used to classify large areas of the river
bottom in terms of sediment properties and that the river bottom depositional types remained
constant. The comparison between side-scan sonar results and PCB levels in shallow
sediments implies that side scan sonar images can be used to estimate both shallow sediment
PCB concentrations and PCB inventories. Hot spot boundaries appeared accurate, although
in some instances hot spot areas needed to be increased to include all nearby areas of high
contamination.

Historical estimates of PCB mass in hot spots below the Thompson Island Dam assumed a
solid specific weight of 1 g/cc . Based on the low resolution core relationship between solid
specific weight and total PCB concentration, more appropriate values of solid specific weight
ranged from 0.5 to 0.79 g/cc for the majority of the 1976-1978 hot spot sample locations.
Applying a solid specific weight based on length-weighted average concentrations yielded
about a 20 to 30 percent decrease in the original PCB inventory estimates. In other words,
the previous calculations of PCB inventories were somewhat overestimated.

Sediments in the near shore environment, which was defined as within 50 feet of the
shoreline, had higher PCB concentrations than estimated in the Phase 1 Report. The Phase 1
Report estimated an exposure point concentration of 66 mg/kg (parts per million) for the 95
percent confidence interval of the arithmetic mean of the shallow sediment concentration
based on the 1984 data, whereas the current estimate would be within the range of 135 to
264 mg/kg. Implications of this change will be addressed in the swimming or wading
exposure scenario in the Human Health Risk Assessment.

Summation

The decrease in PCB inventories in the more contaminated sediments of the Thompson
Island Pool and from several of the studied hot spots below the Thompson Island Dam,
along with the indication of an inventory gain in the coarse sediments of the Thompson Island
Pool, indicate that PCBs are being redistributed within the Hudson River system. These
results show that the stability of the sediment deposits cannot be assured.

Burial of contaminated sediment by cleaner material is not occurring universally. Burial of
more PCB-contaminated sediment by less contaminated sediment has occurred at limited
locations, while significant portions of the PCB inventories at other hot spots have been
re-released to the environment. It is likely that PCBs will continue to be released from Upper
Hudson River sediments.

LOW RESOLUTION SEDIMENT CORING REPORT

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