EPA 520/1-83-018
GEOLOGIC OBSERVATIONS AT THE 2800-METER
RADIOACTIVE WASTE DISPOSAL SITE AND
ASSOCIATED DEEPWATER DUMPSITE 106 (DWD-106)
IN THE ATLANTIC OCEAN
by
Martine Dreyfus Rawson and William B.F. Ryan
Department of Geological Sciences
Lamont-Doherty Geological Observatory
of Columbia University
Palisades, New York 10964
Prepared June 1978
Revised September 1983
This report was prepared as an account of work sponsored
by the U.S. Environmental Protection Agency
under Contract No. 68-01-3933
Project Officer
Robert S. Dyer
Office of Radiation Programs
U.S. Environmental Protection Agency
Washington, D.C. 20460
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FOREWORD
In response to the mandate of Public Law 92-532, the Marine
Protection, Research, and Sanctuaries Act of 1972, as amended, the
Environmental Protection Agency (EPA) has developed a program to
promulgate regulations and criteria to control the ocean disposal of
radioactive wastes. As part of that program, the EPA Office of Radiation
Programs initiated feasibility studies in 1974 to learn whether present
technologies could be used to determine the fate of radioactive wastes
dumped in the past.
In 1975 and 1976, the advanced technologies represented by the
manned deep-submergence research vehicle (DSRV) ALVIN were employed to
perform an on-bottom survey at the Atlantic Ocean deepwater industrial
waste dumpsite (DWD-106) and the previously-used United States low-level
radioactive waste disposal site. DWD-106 is located approximately 170
kilometers (106 miles) offshore at a depth ranging between 1600-2500
meters. The low-level radioactive waste disposal site is located
southwest of DWD-106 approximately 190km (120 miles) offshore at a depth
of approximately 2800 meters (9300 feet). Both sites are situated south
of the axis of the Hudson Canyon channel. The objectives of this survey
were to describe the biological, chemical, geological and physical
oceanographic characteristics of the dumpsites, with the submersible
being used primarily to make direct observations of the geological and
biological conditions at the two dumpsites.
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The present report provides a detailed description of the geological]!
and topographical characteristics of the two dumpsite areas. Three
submersible dives were made in the 2800m low-level radioactive waste
dumpsite and five dives were made at DWD-106. The sediment deposits,
bottom topography, evidence of sediment avalanching, biota, currents, and|
the differences in these parameters between the two dumpsite areas are
discussed. The presence of radioactive waste drums in the 2800m dumpsite|
area is analyzed in terms of the localized geological and physical
processes occurring at the site. The report concludes with a general
discussion of the geologic stability of the two dumpsite areas which
straddle the lower continental slope - upper continental rise provinces.
The Agency invites all readers of this report to send any comments
or suggestions to Mr. David E. Janes, Director, Analysis and Support
Division, Office of Radiation Programs (ANR-461), Environmental
Protection Agency, Washington, D.C. 20460.
Glen L. Sjoblom, Director
Office of Radiation Programs
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TABLE OF CONTENTS
Page
INTRODUCTION [[[ !
SUMMARY [[[ 2
REGIONAL GEOLOGIC SETTING .............................................. 4
Continental Slope ................................................. 7
Continental Rise .................................................. 15
Nature and Composition of the Sediment Cover ...................... 20
THE 1975 SUBMERSIBLE DIVING PROGRAM .................................... 25
THE 1976 SUBMERSIBLE DIVING PROGRAM .................................... 32
CONCLUSIONS AND RECOMMENDATIONS ........................................ 45
UNRESOLVED PROBLEMS [[[ 47
REFERENCES [[[ 50
LIST OF TABLES
1. Location, Depths, and Environment of DSRV ALVIN Dives
of the 1975 EPA Radioactive Waste Disposal Site Survey .......... 28
2. Locations, Depths, Observers, Environment, and Objectives
of DSRV ALVIN Dives of the 1976 EPA Radioactive Waste
Disposal Site Survey ............................................ 35
LIST OF FIGURES
1. Deep-sea core locations and bathymetric contours of the
east coast conti nental margi n ................................... 5
2. Dendritic-type drainage pattern in Heezen Canyon on the
continental slope of New England ................................ 6
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LIST OF FIGURES (Continued)
Page
5. Holes and mounds of biological origin on the upper continental
rise in the northeastern section of Deepwater Dumpsite 106
(DWD-106) 12
6. Position of ancient shore lines on the continental shelf
east of New Jersey and Delaware 14
7. Bathymetric profiles across the continental margin
of the east coast of the United States 16
8. Water mass, sediment, and bottom current structure across
the east coast conti nental margi n 17
9. Distribution of bottom photograph stations showing evidence
of bottom current directions and relative magnitudes 18
10. Umbel Tula deflected in westerly current within a narrow
meandering channel on the upper continental rise 21
11. Lithologies of selected cores from the upper and lower
continental rise seaward of New Jersey and Delaware 23
12. Calcium carbonate contents in surface sediment samples
from the western North Atlantic 26
13. Location of 1975 DSRV ALVIN dives 29
14. Barrel #28 photographed on ALVIN Dive 676 at a depth of
2819 meters 34
15. Bathymetric contours and dive tracks from the 1976 survey on
the southeastern corner of the 2800m low-level radioactive
waste dumpsite 36
16. Encrusting sponges, hydrozoans, and anemones on outcrops of
lithified marlstone 38
17. Partly obliterated sled marks from a 1975 ALVIN dive in the
2800m low-level radioactive waste dumpsite 39
18. Ski marks on the seabed made by DSRV ALVIN 41
19. Large, sub-rounded olistolith lying partly buried within a
slump scar at the southeast corner of the 2800m low-level
radioactive waste dumpsite 42
20. Example of an erosional moat around a corroded and
partly buried drum of radioactive waste 44
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INTRODUCTION
The deepwater radioactive waste dumpsite addressed in this report is an
area of about 100 square nautical miles (342 square kilometers) in the Northwest
Atlantic which lies astride the boundary between the lower continental slope and
upper continental rise of the eastern margin of North America. The dumpsite is
approximately 120 nautical miles east of Cape Henlopen, Delaware. Water depths
at the dumpsite range from about 2500 meters to 2800 meters,. Seafloor relief
is locally smooth, and the site is centered at 38°30'N, 72°06'W.
The general area which is almost contiguous to this radioactive waste
dumpsite is referred to as Deepwater Dumpsite 106 (DWD-106),, Baseline
investigations were initiated in 1974 by the National Oceanic and Atmospheric
Administration (NOAA) which is charged with the responsibility, under
Title II of Public Law 92-532, to investigate the environmental effects of
dumping of waste material into ocean water and onto the seabed.
Geologic field studies of the low-level radioactive waste dumpsite were
undertaken by the U.S. Environmental Protection Agency in the summers of 1974,
1975, and 1976, and involved sampling and bathymetric soundings from surface
vessels, and direct seafloor observation, photography, video recording and
sampling by the manned submersible DSRV ALVIN.
Professor Bruce C. Heezen of Lamont-Doherty Geological Observatory had
responsibility for the 1974 geological investigations at DWD-106 (Heezen, 1975)
and the 1975 and 1976 geological field studies at the low-level radioactive
waste dumpsite. Professor Heezen died in June 1977 prior to final analysis of
the latter field studies. This report has been assembled using field notes,
sketch maps, audiotape recordings made by Professor Heezen, and selected
photographs from the submersible activities of the 1975 and.1976 surveys.
Additional data have been added to this report data from the research files at
Lamont-Doherty Geological Observatory. The assessments and conclusions reflect
the authors' interpretation of the available observations and facts.
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SUMMARY
During 1975 and 1976 a total of eight submersible dives with DSRV ALVIN
were carried out in a relatively small region (about 2 km x 3 km) of the
radioactive waste dumpsite and were centered at 38°30'N and 72°09'W. Six
other dives were distributed through the northern part of DWD-106 near the
boundary of the continental rise/continental slope.
The lower continental slope is incised by submarine canyons debouching
into the northern side of DWD-106. Canyon walls are steep (up to 50°) and
display outcrops of strata made up of calcareous marl stones, grainstones, and
siliceous mudstones. The upper continental rise is incised by narrow meandering
channels. One of them passes through the radioactive waste dumpsite and was
surveyed in detail during the 1976 diving schedule (Heezen and Dyer, 1977).
On the upper continental rise the local terrain is relatively flat but
studded with numerous tracks, trails, holes, and mounds of biological origin.
The sediment carpet is composed of a gray silty-clay referred to in the
pre-1970 literature as lutite. Sediment cores display bioturbation effects
and appear rather homogeneous in lithology and lack distinct bedding. The
carbonate in the dumpsite area ranges between 30% and 43% and averages 37%.
Essentially all of the carbonate is biogenous with foraminifera characterizing
the sand and upper silt-size fractions, and coccoliths characterizing the lower
silt and clay-size fractions (Neiheisel, 1979).
The mineral suite averages 37% biogenous carbonate, 30% clay minerals,
2% mica, 23% quartz, 7% feldspar, 1% detrital heavy minerals, and trace amounts
of glauconite and diatoms. The clay mineral suite is predominantly illite
(50-60%) and generally equal proportions of chlorite and kaolinite which, when
combined, range between 12% and 30%. Montmorillonite comprises between 5% and
10% of the clay minerals. The heavy mineral suite is essentially a garnet-
hornblende suite with a garnet-staurolite ratio similar to the mineral province
on the adjacent continental shelf (Neiheisel, 1979).
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The average sediment texture of the upper and lower portions of the cores
is very uniform over the dumpsite area, with most cores characterized as
clayey-silts and a few as silty-clays.
Pebbles, cobbles, boulders, and large allochthonous blocks (olistoliths)
were encountered on many of the dives. Some of them are interpreted as glacial
erratics, ice-rafted into the area more than 14,000 years ago. Others are
composed of indurated marine marls and clays of Eocene age, carried into
deepwater sites by subaqueous landslides and debris flows in relatively recent
times. In fact, the western part of the dumpsite is a broad slump scar which
has lost tens of meters of sediment cover by creep or fTowage within the time
period since the last major interglacial 35,000 years before present (B.P.).
Bottom currents were detected during a majority of the dives. Five current
meters deployed between August and November 1976 recorded varying oscillatory
currents with a maximum speed of 40 cm/sec and a mean flow of 3-4 cm/sec.
During periods of highest speeds, the currents flowed in a westerly direction
(Hamilton, 1982). Ripple marks were only detected in canyons, gullies, and '
the thalwegs of meandering channels. Scour moats were present around rock
outcrops and waste containers, and the moats were filled with distinctly coarser
lag deposits.
Containers were observed in varying states of integrity. Some of the
containers appeared to have been breached. Encrustations of worm tubes,
anemones, and sponges were seen on the exposed concrete end of the waste
containers and were also common on outcrops of calcareous substrates, indicating
that the abundance of attached organisms is directly related to the solid nature
of the surface of attachment. Mobile fauna (rattail fish, ophiuroids, asteroids,
euphausids, and holothurians) were observed feeding upon surficial sediment
surrounding the waste containers. The rattail fish in particular were attracted
to sediment plumes put into suspension by the submersible. Sessile fauna such
as gorgonians and pennatulids were photographed as they were deflected by
near-bottom currents, the stalked animals being most abundant in flat terrain.
The action of both animals and currents has partly but not totally obliterated
1- to 2-year-old ski marks made by the ALVIN during previous surveys.
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On the continental rise the local terrain is partly hummocky, with relief
of the hills occasionally exceeding 20-30 m. The relief is attributed to
remnant mounds of sediment left behind on broad slump scars. Outcrops are
common on the flanks of some of the hills and on the walls of narrow channels,
but are most pervasive along the outside bends of meanders along the course of
the channels. Gullies on the slope are separated by steeply sloping spurs
draped with clays. Some relict cut and fill bedforms are seen in small outcrops
on the canyon walls where the canyon apparently cuts through older levee deposits.
REGIONAL GEOLOGIC SETTING
The area delineating industrial waste dumpsite 106 (DWD-106) and the nearby
radioactive waste dumpsite covers a diverse seascape of the dissected continental
slope and the depositional terrain of the continental rise. The juncture between
these two seafloor provinces is not particularly sharp because many of the slope
canyons continue onto the rise as channels. Some of the channels pass entirely
through the low-level radioactive waste dumpsite and reach the lower continental
rise and the Hatteras Abyssal Plain.
The slope canyons are evident in the bathymetric contours of Figure 1
adapted from publications of Beatch and Smith (1939), Heezen et al. (1959),
Uchupi (1965), Uchupi and Emery (1967), Pratt (1967, 1968), Holland and Bedding
(1969), Schneider (1970), Emery et al. (1970), and Emery and Uchupi (1972).
The DWD-106 and radioactive waste dumpsite are situated between the Hudson
Canyon System to the northeast and the Wilmington Canyon (sometimes called the
Brandywine Canyon (Schneider, 1970)) to the southwest. The large east-coast
canyons indent the shelf edge and, where surveyed in extreme detail as
illustrated in Figure 2, the canyons display a dendritic-type submarine drainage
system. The dendritic fabric was first recognized by Stetson (1936). Both he
and Shepard (1952) commented on the great similarity of the submarine drainage
network of the east-coast margin with a subaerial "bad!and" type topography
characteristic of North and South Dakota. Although it is widely accepted today
that the submarine features are carved and kept sediment-free by exclusively
subaqueous processes, one should not lose sight of the value gained by the
analogies of Stetson and Shepard as relevant to the landforms of DWD-106 being
sculpted by mechanisms which we do not adequately understand.
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69°
68°
67°
40°
Figure 1. Deepsea core locations and bathymetric contours of the east coast
continental margin. DWD-106 and the smaller contiguous radioactive
waste dumpsite to southeast are outlined; the small solid square
indicates the region of detailed ALVIN submersible surveys. Note
the heavy incising of the continental slope by submarine canyons and
the continuation of the larger canyon systems across the continental
rise. _ Contours are in fathoms (1 fm = 6 ft = 1.8 m). The dumpsite
area is bounded to the northeast by the Hudson Canyon System and to
the south by the Brandywine Canyon System fed from the west by the
Wilmington Canyon. Map is from Schneider (1970). Dotted lines are
survey tracks, primarily of R/V Atlantis and R/V Vema cruises.
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CONTOURS IN
METERS XIOO
Figure 2. Dendritic-type drainage pattern in Heezen Canyon on the continental slope of New England In 19J7>
ALVIN Dives 780, 782, and 783 showed that the slope canyons are routes along which sed merit is actively
transported downslope by debris flows and subaqueous avalanches (figure from Ryan et al., iy/BDj.
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Continental Slope
The Atlantic continental slope is an area of active sediment denudation,
especially for the region from Cape Hatteras northward to Long Island. Forma-
tions which are deeply buried beneath the continental shelf can be traced
seaward by reflection profiling to outcrops along the lower slope. Strata as
old as Upper Cretaceous (65-80 million years) have been recovered in shallow
cores along the slope in the vicinity of Hudson Canyon and off the Carolinas
(Gibson et al., 1968; Fleischer and Fleischer, 1971; Perry et a!., 1975). A
core (#21-38) reported by Stetson (1949) at a depth of 1565 m (855 fathoms) in
the northwestern corner of DWD-106 contains material of Upper Eocene age
(40 million years B.P.).
The outcropping of sedimentary layers along the slope is illustrated in
Figure 3, taken from Grow and Mark! (1977). This profile has been calibrated
to the Hatteras Light No. 1. It shows a seaward extension of Cretaceous age
layers which have been truncated by a major erosion surface (see stars on the
profile) reaching deep beneath the upper wedge of sediment of the continental
rise. Other erosion surfaces also appear on the U.S. Geological Survey (USGS)
Seismic Line #2, passing through the northeast corner of DWD-106, and on USGS
Seismic Line #5, extending southward from Martha's Vineyard.
The extent of these regional unconformities indicates that, a massive amount
of sediment has been removed from the former continental margin and carried
basinward. One of these unconformities is traceable by reflection profiling
techniques to a nearby drillsite of the Deep Sea Drilling Project (DSDP Site 106;
36°26.01'N; 69°27.69'W; 4500 m water depth) reported by Hollister and Ewing
(1972a). This unconformity is called Horizon A by Tucholke and Mountain (1979).
The oldest overlying strata are Miocene in age (<25 million years) indicating
that the vast part of the thick continental rise prism of the western North
Atlantic is remarkably youthful. The erosion surface practically crops out at
the continental rise/slope transition just to the west of DWD-106. Here at
DSDP Site 108 (38°48.27'N; 72°39.2'W; 1845 m water depth), Middle Eocene
(45 million years) sediments have been cored at 35-75 m beneath the seabed
(Hollister and Ewing, 1972b).
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IPOD/USGS LINE
700 800 900
I
00
rviMtiv/n
UNCONFORMITY TERTIARY ' DIAPR COMPLEX
INTERVAL VELOCITIES
IN KM/SEC
Figure 3. Sedimentary outcrops on the continental slope east of Cape Hatteras. The seismic profile and interpretation
is from Grow and Mark! (1977). Tertiary and Cretaceous-age strata are truncated by an erosion surface
whose base (indicated by stars) is now buried beneath the upper continental rise. More than a kilometer or
overburden has been denuded from the continental slope in this region. Outcrops of this type occur in tne
JL.I.. a.
I)uruiwebie
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All the aforementioned evidence emphasizes the "wasted" nature of the
continental slope province. Submarine canyons obviously play an important role
in the progressive landward retreat of the slope. They are not only "bypass"
routes for shelf materials enroute to the continental rise and abyssal plains,
but they are areas of continuing backcutting and denudation (Figure 4).
Erosional processes within the canyons and on the slope which accompanied
fluctuations in Tertiary sea level (to perhaps 60-70 million years B.P.) have
caused a regression in the shelf edge from 10-30 km in this area (Schlee et a!.,
1979). Debris jettisoned into the sea as waste and landing within the confines
of submarine canyons should not be expected to remain for long (geologically
speaking) at the site of impact before being transported into greater depths
on-the continental rise apron.
Submersible explorations carried out by Bruce C. Heezen in Hudson Canyon
and in Oceanographer Canyon (southeast of Cape Cod) have allowed direct
observation of such erosion processes. Recent submersible fieldwork in other
New England canyons (Ryan et al., 1978b) demonstrates that these features are
still actively incising the slope.
The New England canyons in particular contain very narrow axial thalwegs,
in places only a few meters in width, with sheer walls of polished and abraded
lithified sediment. Tidal currents surge in diurnal cycles up and down the
canyons, generally with a modest net upcanyon component. Sediment is carried
into suspension by turbulent eddies and especially by the feeding habits of
bottom dwelling organisms and grazing fish. Diagenetic dissolution, encrusta-
tion, and boring weakens exposed rock faces, eventually producing their collapse
as underwater avalanches. Talus blocks are scattered throughout much of the
canyon channels on the lower slope. Where sand is the dominant sediment on
the adjacent continental shelf, it is fed by current gyres into the canyon heads.
This abrasive material is swept back and forth along the thalweg by the cyclic
tidal currents, thereby amplifying the effects of scouring and undercutting.
Where mud is the dominant lithology on the adjacent shelf, as is the case
in the New York Bight, the abrasive action of tidal currents is reduced.
Photography from submersibles indicates that in the New York Bight visibility is
often less than 2 m due to the high degree of suspended sediment. The mud is being
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o
o
H
CO
0
9 18
NAUTICAL MILES
27
Figure 4. Seismic reflection profile extending across the continental margin from the shelf edge out onto the upper
continental rise to the south of the DWD-106 and radioactive waste dumpsite region. Note how the canyons
on the lower slope and upper rise have cut downward into sediment layers exposing older strata (figure
from Schneider, 1970).
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swept back and forth in each tidal cycle, and tidal currents in excess of
50 cm/sec have, in fact, been measured at 700 m depth in the Hudson Canyon
(Heezen, unpublished). Since sizeable amounts of mud drape the canyon walls
and floor, we conclude that the sediment is not being carried out of the canyon
system presently at a rate greater than it is entering, and entrenchment has
temporarily ceased.
The biological contribution to mass-wasting cannot be overemphasized
(Dillon and Zimmerman, 1970; Warme, 1975; Warme et al., 1971; Palmer, 1976;
Heezen, unpublished field notes). Animal mounds and holes are very common'in
the organic-rich carpet of hemipelagic marls, muds, and mudstones (Figure 5).
Talus ejected from burrows is always thickest on downslope sides of mounds
attesting to a prevailing gravitational migration of excavated material downslope.
Vagrant benthos (crustaceans, holothurians, ophiuroids) are very abundant and
they are constantly creating clouds of suspended sediment. Even the densest
limestones are seen to be bored by polychaete worms and bivalves, lending to
an eventual "swiss-cheese" framework that collapses from lithostatic overburden
pressure and gravity.
The dendritic fabric of much of the canyon networks can be explained by
abrasive activity primarily concentrated in the thalweg. The gradual sediment
entrenchment results in progressive oversteepening of the local thalweg walls.
The mechanical failure of the walls in turn widens the thalweg and perpetrates
lateral collapse. The whole process erodes the slope leading to its retreat.
The dissected regions of the continental slope are therefore only temporary
storage reservoirs for contemporary sediment and/or waste dumped at sea. In
summary, biological, mechanical, and gravitational processes and the prevailing
current regime work in combination to transport materials arriving in the canyon
network to ever greater depths on the slope and rise.
Deep sea drilling was carried out in 1975 on the west African continental
margin on DSDP Leg 47. There, a deep borehole penetrated a massive erosion
surface of a configuration similar to that which exists on the North American
Margin. The drilling (Ryan et al., 1976; Ryan et al., 1979) and integrated
geophysical site surveys (Seibold and Hinz, 1974) confirm that more than
1 kilometer of slope sediment has been removed in only a few million years
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Figure 5. Holes and mounds of biological origin on the upper continental rise
in the northeastern section of DWD-106 about 30 km north of the
designated radioactive waste dumpsite. The holothunans^Psychropotes
depressa) in background are approximately 20 cm in length. Photograph
#4314 is from 1975 ALVIN Dive 591 at 38°55'N, 72°04'W,^and 2460 m
depth The sample basket of the ALVIN submersible is in the foreground.
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(i.e., at rates of tens of centimeters per 1,000 years). However, such
mass-wasting processes are intermittent. There are relatively brief episodes
when deep entrenchment takes place and longer intervals of not only little
entrenchment, but even complete infilling of canyons.
Much remains to be learned about the timing of these episodes and the
processes at work. Nevertheless, there is a growing consensus within the earth
science community that erosive phases of the continental margin seem to have
occurred coincident with times of enhanced sediment bypassing from the
continental shelf to the continental rise (Rona, 1973; King arid Young, 1977).
Lamont-Doherty submersible studies in New England canyons (Ryan et al.,
1978a,b) reveal similar discrete episodes of "cut and fill," the earliest
cutting reaching back at least 40 million years B.P.
i
The most recent significant entrenchment is Quaternary in age, correlating
with the latest phase of northern hemisphere glaciation at approximately
18,000 years B.P. and the accompanying lowering of world-wide sea level (Flint,
1971). The magnitude of relative sea-level lowering along the eastern border-
land has been estimated to be approximately 100 to 130 m (Milliman and Emery,
1968; Dillon and Oldale, 1978), an amount sufficient to move the shore line
eastward to the present shelf-break (Figure 6). The Hudson Channel on the
modern shelf had its origin as a subaerial stream bed (Chelminski and Fray,
1966). The regression caused large thicknesses of sediment to be removed from
the shelf (Garrison, 1970) and strata as old as the Upper Cretaceous were exposed
(Woodworth and Wigglesworth, 1934). Because of the proximity of the shore line
to the shelf edge, rivers were no doubt capable of discharging their bedload
and certainly their suspended load from major floods directly into the heads
of the slope canyons. Where the shelf is narrow as along the coast of southern
France, muddy water may reach abyssal depths in less than a day following river
flooding (Groupe Estocade, 1978). When the heads of the canyons intersect the
near-shore high-energy zone, they capture mud, silt, sand arid sometimes gravel,
boulders and man-made litter, whose downslope flowage, creep, and avalanching
become abrasive agents for further downcutting (Dill, 1962).
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•P-
Figure 6. Position of ancient shore lines on the continental shelf east of New Jersey and Delaware These shore
lines existed at the time of lowered sea level during the last ice age. The continental slope canyons are
thought to have undergone deep entrenchment when the shore line had mgrated out to the shelf edge as was
3 - „ „«„ /•££„..— f*nrn n-JIToM M D anrl R N fllnale- 19/0).
tne case some J/KUUU ' vn.t.~.~----—
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Continental Rise
The continental rise is distinguished from the continental slope by its
more gentle seaward gradient (Heezen et al., 1959). The rise is essentially a
province of net sediment accumulation in contrast to the slope being a province
characterized by denudation.
Off the eastern coast of North America the continental rise contains the
thickest sediment of the central margin (Sheridan, 1974; Mayhew, 1974). South
of Hudson Canyon, the continental rise can be subdivided into an "upper rise"
with regional gradients of 1:200 to 1:600 and with a large, broad, easterly-
sloping convex surface, and a "lower rise" with gradients as low as 1:2500 and
an easterly-facing concave surface (Figure 7).
Groups of small hummocky hills occur in the dumpsite area in the upper
portion of the upper continental rise. The seismic reflection profiles of these
hills give the appearance of large allochthonous blocks (olistoliths) derived
from slumps originating on the steeper continental slope. Characteristic
topographic features of the upper continental rise are steep-walled slump scarps
and meandering channels that cross their surfaces. The lower continental rise
is a broad, nearly level terrace lying at depths generally below 4000 m (2200 fm)
Directly south of Hudson Canyon the terrace is very smooth, having been created
by sediment ponding behind a buried outer ridge which forms part of the lower
continental rise hill complex (Asquith, 1976). The lower continental rise lies
seaward of the dumpsite region and is relevant to our study because it is a
site of deposition for materials which may be transported from the dumpsite
region by channelized turbulent flow and/or subaqueous avalanches. Some channels
which meander through the dumpsite continue across the lower continental rise
and through the lower continental rise hills province to debouch near the
northeastern limit of the Hatteras Abyssal Plain.
The continental rise lies beneath the path of the Western Boundary
Undercurrent of the North Atlantic (Heezen et al., 1966; Schneider and Heezen
1966; Schneider, 1970). The boundary current (Figure 8) is part of the North'
Atlantic Deep Water (Swallow and Worthington, 1961) which flows southward
parallel to regional isobaths. Its movement, shown in Figure 9, has been
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LOWER CONTINENTAL
RISE
LOWER CONTINENTAL
RISE HILLS
LOWER CONTINENTAL
RISE
HATTERAS O. Rl DGE
L. CONTINENTAL
_ HILLS
tt ATTFR AS
T. CANYON HATTERAS ABYSSAL PLAIN
RMUDA RISE
BLAKE BAHAMA
OUTER RIDGE
BLAKE BAHAMA
ABYSSAL PLAIN
Fiaure 7 Bathymetric profiles across the continental margin of the eastern
9 roast of the United States. DWD-106 and the radioactnve waste
dSSslte are siluated on Profile A in an area where the continental
Hse Is particulaHy broad and where it can be differentiated into
«i »miner rise" with a typical convex surface and a more gently
diDDiFlower rise " The dumpsite area straddles the limit between
SKpVr rise" and the continental slope. Vertica exaggeration
of the profiles is 1:100 (figure from Schneider, 1970).
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Figure 8. Section across the continental margin passing through DWD-106 and
the radioactive waste dumpsite. This illustration from Schneider
(1970) shows potential temperature of the water column, evidence,
magnitude, and direction of near-bottom currents, bathymetric profile,
character of the acoustic echo return from the seafloor, and surface
sediment characteristics. Strong currents occur below the change in
bottom gradient that distinguishes the "upper rise" from the "lower
rise." The boundary circulation causes cold-water isotherms (<2°C)
to intrude onto the continental rise. Prolonged bottom echo sequences
and an increase in the sand- and silt-sized surface sediments are
associated with current-swept zones. DWD-106 and the radioactive
waste dumpsite are situated landward (to left) and above the Western
Boundary Undercurrent in a region where deep-water circulation at
present is considerably less vigorous.
-17-
-------
CO
NEW YORK
KMS CONTINENTAL
0. SHELF
ZUJ
UIQ.
zo
UPPER
CONTINENTAL
RISE
r"ULFSTREAM
LOWER
\ CONTINENTAL
\ RISE
BERMUDA
RISE
ABYSSAL
PLAIN
SLOPE
WATER
NORTH ATLANTIC DEEP WATER
NO CURRENT EVIDENCE
SMOOTH BOTTOM
(NO CURRENT DIRECTION]
WEAK CURRENTS
STRONG CURRENTS
VERY STRONG CURRENTS
CLEAR WATER
SLIGHTLY MUDDY WATER
(a) Q MUDDY WATER
IRREGULAR
PROLONGED
ECHO
STRONG ECHO
WITH CONVERGING
SUBBOTTOM
ECHO
ECHOGRAM
CHARACTER
VERY STRONG SINGLE
ECHO
-/YYW\
PROLONGED ECHOS WITH SUBBOTTOMS
SUBBOTTOM
BROAD HYPERBOLA
SINGLE ECHO WITH INTERMITTANT SUBBOTTOM
IRREGULAR'
PROLONGED ECHO
(OUTCROP)
100-
ICOARSE siLT
ymg
<62.0|J
-------
Figure 9. Distribution of bottom photograph stations which show evidence of
bottom current direction and relative current speed (map from
Schneider, 1970). "M" designates muddy bottom. Arrows without
circles show current flow as determined from the tracking of
neutrally-buoyant floats. Contours in fathoms. Note the persistent
southwesterly direction of the Western Boundary Undercurrent transport
on the lower continental rise (below 2200 fm, or 4000 m) and the lack
of a detectable current on the upper rise, especially near and within
the locality of DWD-106 and the radioactive waste dumpsite.
-19-
-------
detected by direct current measurements (Volkmann, 1962) and hundreds of
compass-oriented photographic stations (Heezen and Hoi lister, 1971). These
photographs taken in the 1976 ALVIN survey provide distinct evidence of
current-swept and current-free zones on the bottom revealed by features such
as corrugations, ripples, crag and tail structures, furrows, and inclined stalks
of attached epifauna (Figure 10). The most common evidence of bottom currents
is reflected in the small-scale relief features on the bottom. Smooth, round,
mud ripples (wavelength 2-6 m) are observed in some of the photographs. Linguoid
(tongue-shaped) and transverse ripples are bedforms most commonly seen in photo-
graphs. Steep lee and gentle stoss slopes indicate the direction of the
unidirectional current flow to the southwest.
Nature and Composition of the Sediment Cover
The Lamont-Doherty deep sea core repository contains numerous cores from
the region surrounding and within DWD-106 (for example, see station locations
plotted in Figure 1). The most thorough published descriptions of a large
number of these cores can be found in Ericson et al. (1961).
Two distinct sediment types characterize the continental slope. Cores
from the thalwegs of major submarine canyons contain coarse elastics (sometimes
including gravel and large fragmented mollusk shells). These clastic beds
generally contain micro- and macrofauna reworked and displaced from areas of
the shallow shelf. The elastics are in the process of being transported through
the canyon systems onto the abyssal plain. Cores between the canyons consist
of cohesive dark greenish-gray silty-clays with high organic carbon contents.
These sediments are low in calcium carbonate, contain some glauconite, are rich
in pyrite, and sometimes are abundant in siliceous microfossils such as diatom
frustules. The lack of appreciable stratification in the silty-clay cores
suggests deposition under rather steady environmental conditions without signif-
icant winnowing by currents. Carbon contents in excess of 1.5% by weight are
related to the presence of low oxygen contents in the mid-water column along
the continental slope (see Jones, 1983). Outcrops of pre-Recent (i.e., before
11,000 years B.P.) and pre-Pleistocene age claystone and shale indicate erosion
of the slope and displacement of part of its uppermost sedimentary cover.
-20-
-------
Figure 10. Umbellula. a deepsea octocoral, is shown here deflected in a westerly
current within a narrow meandering channel on the upper continental
rise at 38°30.51'N, 72°09.28'W, water depth 2788 m. The Umbellula
is about 40 cm in height and the current velocity can be estimated
to exceed 10 cm/sec. Note smoothing of the regionally flat, gray,
silty-clay bottom. This photograph was taken during ALVIN Dive 676
within the low-level radioactive waste disposal site.
-21-
-------
The upper continental rise is characterized by homogeneous gray to light-
brown colored clays and silty-clays that are significantly more bioturbated
than the slope cores. Carbonate contents in the area of DWD-106 and the
radioactive waste dumpsite approach 15% to 30% and organic carbon contents are
less than 0.4%, indicating effective biological reworking of these sediments.
Cores rarely contain pre-Pleistocene age sediment, except as clasts within
debris flow deposits. Core A164-1, located just east of DWD-106 and the radio-
active waste dumpsite (Figure 1) and southwest of the Hudson Canyon system,
has been subjected to biostratigraphic analysis. This core is 8.69 m in length
and consists for the most part of homogeneous silty-clay interbedded with a
few graded sand and/or silt layers, whose frequency of occurrence increases
with increasing depth within the core. On the basis of the abundance of the
planktonic foraminifera Globorotalia menardi1, Ericson et al. (1961) established
biostratigraphic zones which delineate Recent (Holocene) sediments (Z Zone)
from those of the last glacial epoch (Y Zone). The boundary between these two
Zones has been dated at 11,000 years B.P., and it occurs at a depth of 75 cm
in the core. Calculations of sedimentation rates based upon the location of
this boundary yield a rate of 6.8 cm per 1,000 years for Holocene deposition.
The sedimentation rate of the lower (glacial) section is greater than twice
that of the upper 75 cm, reflecting an increase of coarse sediment delivered to
the canyon system through subaqueous landslides and debris flows during glacial
times (Ericson et al., 1961).
Sediments on the upper continental rise are essentially hemipelagic
deposits consisting of skeletal material of marine plankton admixed with clay
minerals, fine quartz and feldspar derived from the adjacent coastal plain and
shelf. Their distinct homogeneity (Figure 11) points toward a relatively
tranquil environment into which coarser silts and sands have not been signifi-
cantly advected laterally by either traction currents or suspension bedloads.
For the most part, the coarse-grained sediments apparently bypass the upper
rise by means of canyons and channels where they are confined almost exclu-
sively to the narrow axial thalwegs and the adjacent levees. However, a study
of the sediment heavy minerals and size fractions, including percent of
sand-size inorganic minerals, at the Atlantic 2800 m radioactive waste dumpsite
suggests that some coarse silt and sand is derived from turbidity flows spilling
-22-
-------
Figure 11. Lithologies of selected cores from the upper and lower continental
rise seaward of New Jersey and Delaware. DWD-106 and the radioactive
waste dumpsite would be characterized by the type of surficial
sediment found in Cores V19-1, A167-1, and A185-60 (see Figure 1)
which is homogeneous with little distinct bedding. Some winnowing
is evident by the presence of thin beds of foraminiferal sands
such as those occurring in Core V19-1.
-23-
-------
o
o
m
m
i z
£
CONTINENTAL
SLOPE
o
o
m
m
o
o
mm™
I
LOWER
CONTINENTAL
RISE
HILLS
-gOD
r-<
z>
CD
m
00
m
c.
o
i of] a ||l!!iil!lli!!fii!iig i i!ij[[||Tll!l!i!!i!!i III! il!!lliaaii!l«»!iJillll!liffi!3niRan![
I 1 1 1 1 1 1
-------
out of the channels and being transported westward by the contour currents
(Neiheisel, 1979).
The lower continental rise is essentially covered by noticeably light-
colored brown to tan clays and silty-clays in which there are numerous interbeds
of thin well-sorted, ungraded and often ripple-laminated silts and fine sands
(Hubert, 1964; Hollister, 1967). A distinct feature of the lower continental
rise sediments is the occurrence of bands of bright red clay (Figure 11) derived
from Upper Carboniferous red silts of the Gulf of St. Lawrence which have been
transported southward by the Western Boundary Undercurrent (Conolly et al.,
1967; Needham et al., 1969).
The overwhelmingly stratified nature of the lower continental rise sediments
indicates the presence of dynamic and variable sediment processes at these depths
(Schneider, 1970). The laminations of well-sorted silt are interpreted as trac-
tion deposits laid down by the southwesterly flowing Western Boundary Under-
current which derives its material from turbidity currents passing across the
rise enroute to the abyssal plain. The light color of the sediment provides
evidence of a persistent, well-oxidized benthic boundary layer, and higher
calcium carbonate contents (see Figure 12) indicate less dilution of biogenic
skeletal material in the pelagic layers by clay minerals of terrestrial origin.
THE 1975 SUBMERSIBLE DIVING PROGRAM
During July and August of 1975, nine dives were conducted with DSRV ALVIN
on the continental margin east of the Maryland-Delaware coast (Table 1). The
purpose of the program was to study DWD-106 and the low-level radioactive
waste dumpsite in order to describe the chemical, biological, physical, and
geological characteristics of these sites and to initially determine the effects,
if any, of dumping on the environment.
The survey was conducted in an area bounded by the coordinates 38°30'N,
39°10'N and 71°55'W and 72°34'W, which encompasses the lower continental slope
and the upper continental rise provinces of the continental margin. Dives 586,
587, 589, and 590 were made in the shallower northwest quadrants of the dive
area where the slope is incised by small canyons (Figure 13). Dive 587 traversed
-25-
-------
Figure 12 Calcium carbonate content in surface sediment samples from the
western North Atlantic (map from Schneider, 1970). DWD-106 and the
radioactive waste dumpsite contain relatively low carbonate contents
(20-30%) characteristic of continental slope and upper continental
rise sediments which are heavily diluted by fine-grained, inorganic
minerals transported seaward from the adjacent continental coastal
plain.
-26-
-------
80°
PERCENTAGE OF
CARBONATE IN
SURFACE SAMPLES
-27-
-------
TABLE 1 - LOCATIONS, DEPTHS, AND ENVIRONMENT OF DSRV ALVIN DIVES DURING THE 1975 NOAA-EPA
SURVEY AT THE DWD-106 AND 2800 m RADIOACTIVE WASTE DISPOSAL SITES
00
I
Dive No. Date Latitude
583 7-25-75 38°33'N
584 7-26-75 38°30'N
585 7-27-75 38°30'N
Longitude
72°12'W
72°09'W
72°09'W
Depth On Bottom Leave Bottom Bottom Environment
2786m 1153 hours 1753 hours
2806m-2829m 1338 hours 1630 hours
2818m-2832m 1216 hours 1710 hours
586 7-28-75 38°45'N 72°31'W 2318m-2340m 1153 hours 1430 hours
587 7-29-75 38°50'N 72°34'W 2027m-2148m 1100 hours 1410 hours
589 7-31-75 38°52'N 72°16'W 2400m-2452m 1339 hours 1808 hours
590 8-1-75 38°56'N 72°26'W 1688m-1833m 1208 hours 1810 hours
591 8-2-75 38°55'N
592 8-3-75 39°10'N
72°04'W
71°55'W
2440m-2477m 1050 hours 1706 hours
1930m-1982m 0741 hours 1159 hours
Many containers, munitions, etc., scattered throughout area. Gentle
hills, depressions, and 10 m high erosional escarpments, with abundant
encrusting organisms. A few scattered boulders, some of which may be
glacial erratics.
Common boulders on soft gray silty-clay.
Discovered some damaged low-level radioactive waste drums, and cored
sediment in close vicinity.
Terrain relatively flat with low hummocks, mounds, and depressions of
biological origin. An occasional small rock sighted. Slight westerly
flowing current.
Terrain dissected by gullies some 2 to 12 m across and up to 15 m deep
or more. Gully floors are flat with abundant animal life resting on
thin layer of pale gray sediment covering a more dense, sticky bluish
sediment below. Canyon walls display outcrops of whitish marl.
Flat terrain with few hills and hummocks. Little current. Small rocks
and boulders greater than 1 m in diameter on sediment. Abundant
"fairy rings."
Relatively flat at point of descent, a few mounds, hills, and hummocks.
Some outcrops and projecting ledge of stiff clay. Outcrops of indurated
light marl stone. Some escarpments and high spurs.
Quite flat bottom. No ripple marks and little evidence of current.
Some scattered rocks encrusted with sponges. Clay outcrops.
Partly flat and partly steep. Some ripple marks. Rounded hillocks
and outcrops of "nodular" sediments. Gravel and cobble with occasional
sponges and worm tubes. A rounded marlstone was collected (Eocene
in age).
-------
Figure 13. Locations of the 1975 DSRV ALVIN dives within the Atlantic 2800 m
radioactive waste dumpsite (Dives 583, 584, 585) and the adjacent
DWD-106 (Dives 586, 587, 589, 590, 591). This figure is an enlarged
segment of Figure 1, with contours in fathoms (1 fm = approximately
1.87 m).
-29-
-------
-oe-
-------
a terrain dissected by three gullies 2-12 m in width and up to 15 m deep. The
canyon floors were quite flat and supported an abundant epifauna. A thin layer
of pale-gray surficial sediment, overlying a,bluish sticky sediment, was covered
by faint tracks and trails made by echinoderms, holothurians, and crustaceans.
The walls of the canyons had slopes varying from 50° to nearly vertical.
Erosion of the canyon walls is evidenced by the occurrence of pieces of wall
rock, ranging in size from small fragments to slabs 2-3 m long, scattered on
the canyon floor. Some were covered with a light dusting of sediment while
others were free of any sedimentary material. Brittle stars, branching
gorgonians, large sponges, and other fauna were present on the canyon walls
which, in some locations, consisted of a whitish marl.
Dive 589 in 2400-2452 mjof water took place in a region of relatively flat
terrain, with little or no current, and few hills and hummocks. Small rocks,
cobbles, and boulders up to 2 m in diameter were seen littering the ocean floor
surface. Asteroids, echinoids, sea feathers, and "fairy ring" markings in the
sediment were abundant, denoting extensive biological activity on the sediment
surface.
Dive 590 encountered a few mounds, hills, and hummocks, within a relatively
flat terrain. The sediment surface showed pits, mounds, tracks, and trails of
biological origin with echinoids, holothurians, ophiuroids, and ceranthid
anemones being fairly common. Outcrops of indurated light marl stone, escarpments
(up to 20 m in relief), and high spurs were seen.
Dives 583, 584, and 585 took place on the upper continental rise at depths
around 2800 m in the low-level radioactive waste dumpsite. On Dive 583, many
containers, munitions boxes, and other debris were seen scattered throughout the
areas. Surface morphology varied during the bottom traverse ranging from flat
terrain to gentle hills and depressions with 12 m high clay cliffs covered by
abundant attached fauna. Small to very large granite boulders were observed;
some exhibited sparse attached growth while others were devoid of encrusting fauna.
These rocks were most likely carried to this region by ice-rafting during glacial
epochs. Sediment close to a radioactive waste container was cored on Dive 585.
A relatively flat terrain with relief in the form of low hummocks, mounds, and
depressions of biological origin was traversed on Dive 586 in a region slightly
-31-
-------
north and west of the previous three dives (Figure 13). The sediment here was
sticky and showed no ripple marks although a slight westerly flowing current
was observed. Occasional small rocks littered the surface of the sediment.
Dive 591 in the northeast corner of the dive quadrant transected a
featureless area of little relief. No ripple marks were observed and there
was little evidence of an active current at the time of the dive. As the ALVIN
submersible traversed the bottom, relief increased to 3-4 m giving the visual
impression of small hills and depressions. Sponges were present on occasional
outcrops; some ophiuroids, holothurians, and sea urchins were observed and
photographed.
Dive 592, north and east of the preceding dive area, was in a region of
alternating flat relief, dimpled with a few shallow depressions and mounds,
and steep relief displaying outcrops. A 0.8 knot (40 cm/sec) current was
measured in a region of current ripples where the depressions were shallower
and the hillocks were rounded. Outcrops of "nodular" sediment were seen which
are interpreted to be highly calcarous by analogy to rocks of similar appearance
caused by weathering in terrestrial outcrops. Gravel and cobbles with occa-
sional attached sponges and worm tubes typified the sediment surface. A rounded
cobble of marl stone was collected and subsequently determined to be Middle
Eocene in age.
THE 1976 SUBMERSIBLE DIVING PROGRAM
During the summer of 1976, another U.S. Environmental Protection Agency
radioactive waste dumpsite survey was conducted in the 2800 m low-level radio-
active waste dumpsite located southeast of DWD-106. The survey was centered
at coordinates 38°30'N, 72°09'W, a position on the upper continental rise
approximately 120 miles (190 km) east of the Maryland-Delaware coast.
The survey consisted of five deep submersible dives employing the ALVIN to
search for a variety of radioactive waste containers disposed of in the dumpsite
area, to record the geological and biological characteristics along each dive
traverse, and to collect accurately-positioned sediment samples near low-level
radioactive waste packages. One 80-gallon low-level radioactive waste drum was
-32-
-------
recovered from a depth of 2819 m (Figure 14)_pn July 31, 1976. Four bottom-
moored vector-averaging current meters were deployed, one at each of the corners
of the dumpsite area to make a 3-month measurement of the direction and speed of
bottom-water transport at a distance of 6 m above the seabed. The mooring in
the southwest corner of the dumpsite had an additional current meter at a
distance of 96 m off the bottom. The findings of this current meter mooring
experiment are detailed in another U.S. Environmental Protection Agency report
(Hamilton, 1982). The principle conclusion of that report was that southwesterly
mean currents of 3-4 cm/sec were flowing near the bottom, and the low frequency
part of the spectrum was dominated by fluctuations around a 16-day period which
could be explained as bottom-trapped topographic Rossby waves with horizontal
wavelengths of about 200 km.
The southwest corner of the Atlantic 2800 m dumpsite had been previously
examined by DSRV ALVIN in 1975. Dives 584 and 585 during July 1975 had located
more than half a dozen radioactive waste drums partly buried in the sediment
cover near 38°30.0'N and 72°09.3'W. One of these drums, found at 1300 hours,
July 27, 1975, during Dive 585 was selected for the 1976 recovery operation. The
drums sighted in 1975 were scattered over an area of only about 150 m in diameter.
Therefore, the 1976 field investigations required accurate navigation of the
submersible, which was accomplished using bottom-moored acoustic transponders.
The 1976 field program comprised five dives (676-680) between July 29 and
August 3. The locations of the dives are given in Table 2, arid the dive tracks
and locations are plotted in Figure 15 (Heezen and Dyer, 1977). The first four
dives explored the seabed in the general vicinity of two of the 1975 dives where
waste drums had been sighted. The final dive to the west of the previous dives
undertook a lengthy reconnaissance track parallel to the regional contours.
A detailed bathymetric survey carried out with precision acoustic naviga-
tion revealed the radioactive waste containers to be scattered within a broad
amphitheatre-shaped depression characterized by hummocky relief. The dumpsite
was crossed by a rather narrow (<100 m wide, 5-20 m deep) channel, which displayed
large meanders (Heezen and Dyer, 1977). The broad depression is a slump scar
created by the downslope flowage or creep of a 15 to 20 m thick cover of sediment
(Embley, 1976). The small hills in the dive area are interpreted to be remnants
-33-
-------
$f?pr ^ ^:~rf~?;';:
Figure 14. Barrel #28 photographed on Dive 676, July 29, 1976, at a depth of
2819 m. A retrieval harness was put on the barrel in preparation
for its recovery. The barrel had been partly buried in the seabed
for about 15 years. Scour marks show a net current streaking of
sediment in the southwest direction. The original disturbance to
the seabed made by impact of this waste container has been smoothed
and mostly obliterated by the bottom current.
-34-
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TABLE 2 - LOCATIONS, DEPTHS, OBSERVERS, ENVIRONMENT AND OBJECTIVES OF DSRV ALVIN
DIVES OF THE 1976 EPA 2800 m RADIOACTIVE WASTE DISPOSAL SITE SURVEY
Time of
Arrival
Dive on
No. Bottom Latitude
Longitude
Depart
Bottom
Depth (Time) Latitude
Longitude
Scientific
Depth Observers
676 1230
hours
38°30.57'N 72°09.32'W 2774m 1900
hours
677
678
1242
hours
1235
hours
38°30.17'N 72°09.10'W 2778m
38°30.35'N 72°09.31'W 2788m
1856
hours
1834
hours
679
1125
hours
38°30.25'N 72°09.42'W 2787m
1803
hours
680
1243
hours
38°30.15'N 72°10.71'W 2767m
1645
hours
38°30.33'N 72°09.02'W 2773m Robert Dyer
and
Bruce Heezen
38°30.33'N 72°08.92'W 2805m
38°30.49'N 72°09.36'W 2788m
38°29.93'N 72°09.20'W 2780m Robert Dyer
and
Bottom Environment
Smooth light gray silty sedi-
ment, pock-marked by benthic
organisms. Previous years
ALVIN sled marks still evident.
Some outcropping strata along
about 5% of traverse. Current
about 5 cm/sec to SSW.
Much debris lying on soft gray
partly bioturbated sediment.
A few outcrops of light-
colored marls, well-rounded.
Crossed some hummocky terrain.
Light current to SSW.
Numerous barrels and ammuni-
tion containers scattered in
and between some small ravines
cut into a silty-clay sub-
strate. Outcrop sampled is a
white chalk covered with
sponges.
Flat, silty-clay terrain with
numerous tracks, "fairy rings,"
Pamela Polloni mounds, and depressions of
biological origin. One large
allochthonous boulder, riddled
with holes and encrusted with
hydrozoans, anemones, etc.
White chalk outcrop sampled.
Bruce Heezen
and
Kip Durrin
Robert Dyer
and
Bruce Heezen
38°30.67'N 72°09.80'W 2765m Robert Dyer
and
Akihiko Ito
Flat unchanneled area to west
of previous dives. Gray
silty-clay with single small
outcrop. Much evidence of
benthic life.
Objective
Locate and examine radioactive
waste containers, collect envi-
ronmental samples, attach line
and pinger to waste container
for future recovery.
Attach line to radioactive
waste barrel and to retrieval
clamp. Search for additional
barrels and conduct dye pellet
experiment.
Collect surface sediment sam-
ples with core tube at several
distances from a radioactive
waste drum. Explore for more
containers and obtain a sample
of outcrop material.
Conduct biological survey and
collect box cores of surface
sediment. Sample outcrop.
Search for more barrels and
collect cores for radiochemical
and infaunal analyses.
-------
I
00
o\
I
MEANDERING CHANNEL. UPPER CONTINENTAL RISE
ALVIN DIVES 676 -680
July29-Aug.3 1976
• • ALVIN track
LULU track
A outcrop
Control by bottom deployed transponder net
Geodetic position by LORAN -
Isobaths in meters
Figure 15. Bathymetric contours (in meters) describing a meandering channel (orange color) on the upper continental
rise observed during the 1976 DSRV ALVIN submersible survey in the southwestern corner of the 2800 m
low-level radioactive waste dumpsite. ALVIN tracks for Dives 676-680 are also shown (Heezen and Dyer,
1977). Navigation of the survey lines and on-bottom traverses of the submersible were controlled by
acoustic ranaina to bottom-moored transoonders.
-------
of the original cover left behind within the slump scar. The tracks of
Dives 676, 677, 678, and 679 cross over these small hills and the flanks
frequently expose strata of pre-Recent age. Most of the outcrops were covered
with encrusting sponges, worm tubes, hydrozoans, and anemones (Figure 16).
Very little modern sediment was observed covering the outcrojps, suggesting that
recent erosion has occurred in the area despite an average regional sedimenta-
tion rate in excess of 5 cm per 1,000 yrs (Ericson et al., 1961). This lack
of an appreciable post-Pleistocene sediment cover is somewhat contradictory to
the tranquil environment observed from the submersible.
The seabed between outcrops is composed of a smooth-surfaced gray silty-
clay and shows no consistent current lineation. Sediment stirred up by the
skis of the DSRV ALVIN was seen to move to the southwest with a velocity of
approximately 10-15 cm/sec, which is weak compared to currents observed in many
submarine canyons on the slope (Ryan et al., 1978b), or compared to the Western
Boundary Undercurrent on the lower continental rise. Isolated sedimentary
blocks and low-level radioactive waste containers lie both inside and outside
the meandering channel and they are surrounded by well-formed scour moats
approximately 20 cm in depth.
Sled marks made by ALVIN the previous year (1975) were discernible although
the edges of the sled tracks had collapsed and had been partly obliterated by
currents and animals (Figure 17). The presence of stalked filter feeders bent
in the direction of current flow (Figure 10) indicates that currents were
present. Although the currents have been too gentle for the generation of mud
ripples, they were sufficiently strong to smooth the sediment. However, the
thinness of sediment cover on the outcrops as well as the presence of scour
moats seem to indicate that the area is periodically swept by powerful currents.
The smooth surface of the sediment is marred by tracks and trails, brittle star
impressions, animal "volcanoes," and circles of small holes known as "fairy rings"
(some of which cut across the previous ALVIN tracks). Although large holothurians
were present and fresh feces were observed, no old feces could be detected
suggesting that they are destroyed by bioturbation or currents.
-37-
-------
Figure 16. Encrusting sponges, hydrozoans, and anemones on outcrops of
marl stone around the flank of an erosion remnant hill at 38 30.33 N
72°09 04'W This photograph is from ALVIN Dive 678 in the low-level
radioactive waste dumpsite at a depth of 2778 m and shows the very
thin dusting of recent sediment on the exposure of much older
material. Note the heavily bored nature of the marl stone.
-38-
-------
Figure 17.
Partly obliterated ALVIN sled marks of previous year (1975) infilled
by darker sediment. Note the fractured and friable nature of a
semi-compacted disturbed light-colored silty marl. Rattail fish in
foreground (Cpryphaenoides sp.) is approximately 35 cm in length
Photograph taken at 2778 m depth during ALVIN Dive 677 in the
low-level radioactive waste dumpsite near 38°30.28'N, 72°09.01'W.
-39-
-------
The abundance of fauna on the bottom demonstrates that the low-level
radioactive waste dumpsite is a biologically active area. The most common
organisms observed were sponges, worms, gorgonians, ophiuroids, asteroids,
decapods, rattail fish (Corvphaenoides sjx), tunicates, sea pens, anemones,
and holothurians. Rattail fish were attracted to the sediment stirred up by
the ALVIN and were often observed to be feeding on sediment resuspended by the
submersible (Figure 18). Occasional similar behavior was also noted in various
starfish and shrimp.
Encrusting organisms were scarce on many of the drums although outcrops
in the area were covered with such organisms. The scarcity of encrusting fauna
may be attributed to either flaking rust on the surface of some containers which
does not provide a firm substrate for attachment, or to the inhibition of
encrusting organisms by corrosion products. Encrustations were generally
observed to be more common on the exposed concrete end of the containers than
on the flaking metal sides.
The southeast corner of DWD-106 and the north, central, and western
portions of the low-level radioactive waste dumpsite are partly littered with
allochthonous blocks of a wide range of sizes composed of indurated sedimentary
material carried into the area by subaqueous landslides (i.e., debris flows).
Several blocks were encountered during Dives 676 and 678, particularly one
massive block several meters in diameter at 38°30.43'N, 72°09.18'W (Dive 676)
which is shown from two vantage points in Figure 19. Another somewhat smaller
block sampled during Dive 678 consisted of calcareous grainstone of Middle
Eocene age (40-43 million years B.P.). Based on the examined fauna! content
and sediment composition, the grainstone was most likely laid down originally
in an outer-shelf, high-energy environment and subsequently carried to the
deeper depths of the dumpsite area.
The allochthonous blocks and other substrate outcrops (particularly along the
wall of the meandering channel) act as strong acoustic targets for the forward-
looking CTFM (Continuous Transmission, Frequency Modulated) sonar aboard the
ALVIN. These blocks lie on and within a semi-firm silty-clay and range in size
from pebbles to masses larger than the ALVIN submersible itself. Many of them
are buried to a depth of about half their diameter which is not greatly different
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Figure 18. Sled marks on the seabed made by DSRV ALVIN and photographed during
Dive 678 at a depth of 2780 m in the low-level radioactive waste
dumpsite. Rattail fish (Coryphaenoides sp.) were commonly observed
to feed within the sediment which had been freshly disturbed during
the ALVIN traverse.
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Figure 19. Large sub-rounded olistolith lying partly buried within a slump
scar at the 2800 m low-level radioactive waste dumpsite. This
allochthonous block of marl, photographed at 2775 m on ALVIN Dive 676,
is several meters in diameter and only lightly dusted with sediment.
It and numerous other similar blocks were carried into the area in the
recent past by a subaqueous landslide originating on the continental
slope some 60 to 70 km to the northwest. Note the numerous small
attached translucent alcyonaceans, Eunephthya fruticosa, particularly
evident on the top surface of the marl block in the upper photograph.
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from the radioactive waste drums that were jettisoned into the area from the
sea surface.
Tube cores taken near the drum encountered on Dive 678 and selected for
recovery could be readily inserted into the silty-clay up to their total
length of about 40 cm. The cores were, however, somewhat difficult to extract,
suggesting that the clay there has a relatively high cohesive strength.
Most of the drums and some of the allochthonous blocks contained no
sediment film or only a very thin dusting. The lack of sedimentation on the
tops of the drums is probably caused by the same currents which have scoured
broad moats around them. These moats contain coarse-grained lag deposits which
give the sediment cover a locally darker texture (Figure 20). In all photo-
graphs of drums studied, the metal surfaces were rusted, with flakes of rust
peeling away and littering the adjacent sediment surface with an orange film
(Figure 20). In the vicinity of the drums the bottom mud seemed browner than
usual -- a feature which might be the result of the deposition of rust flakes
from the surface of the drums. The rust in the sediment seems to be oriented
in a southwesterly direction which correlates with the prevailing current
direction. The rust variably caused a discoloration of the sediment to a
distance of 30 to 50 cm from the containers.
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Figure 20. Example of an erosional moat around a corroded and partly buried
drum of radioactive waste encountered at 2774 m during ALVIN Dive 676.
Flaking of rust has stained the adjacent surface sediment. The moat
has collected a distinctly coarser-textured lag deposit of winnowed
pteropod tests and fine gravel, swept in streaks in a southwesterly
direction along with the iron oxide flakes.
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CONCLUSIONS AND RECOMMENDATIONS
Conclusions
DWD-106 and the adjacent 2800 m low-level radioactive waste dumpsite
occupy a seascape subject to flushing by major natural disturbances such as
subaqueous avalanching, debris flows, and turbulent gravity-propelled sediment
suspensions. The few available piston cores from the Lamont-Doherty repository
which have been recovered from this area indicate an intact Holocene section,
partly winnowed, but not removed by slumping. Seismic profiles show extensive
gullying which, in the slope area, has cut down into 50 million year old hori-
zons exposing them as outcrops. The extensive denudation of the continental
slope and uppermost rise is confirmed by deepsea drilling at DSDP Site 108,
immediately to the west of the dumpsite area. Low-level radioactive waste
packages, ammunition boxes, and other debris resting on the seafloor could be
subject to remobilization seaward by flushing events. Submersible surveys
showed the present environment to be both locally eroding (base of escarpments,
moats around outcrops, thalwegs of gullies and channels) and locally depositing.-
The study of piston cores indicates rates of sedimentation exceeding 5 cm per
1,000 years. Hence, many of the waste packages could be buried or nearly
buried in some 20,000 years.
Despite the inevitability of shallow burial of objects through sediment
deposition, portions of the low-level radioactive waste dumpsite could be exhumed
by another debris flow of the magnitude which created the slump-scar character-
istic of the 1976 dive area, where 10-20 m of sediment were removed.
Recommendations
The dumpsite area should be more systematically sampled by long cores
(5 m or more in length) and/or subsurface drilling. There is a need for
comprehensive stratigraphic studies to measure rates of sediment accumulation,
the extent of contemporary winnowing of sediment, and, in particular, the
frequency of past episodic events which upon reoccurrence will scatter and/or
bury debris littering the dumpsite area. The cores need to have a record of
at least 100,000 years and preferably 500,000 or more years in order to provide
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some statistical insight into the repetition and nature of strati graphic
unconformities that are the record of natural flushings. Studies should
include biozonation, isotopic and paleomagnetic stratigraphy, radon and thorium
geochemistry, and 14C radiochronology.
Much additional accurately-navigated bathymetry and near-bottom, side-scan
sonar profiling should be accomplished in order to work out the areal distribu-
tion of gullies, meandering channels, slump scars, and remnant hills. A high
priority would be to request the cooperation of the Oceanographer of the Navy
to provide a multi-beam sonar survey of the dumpsite area.
As a long-range objective we recommend instrumenting the dumpsite area
with seismic monitors, tilt-meters, radiation counters, and nephelometers to
permit recording of natural disturbances over the period of decades. There is
little likelihood of witnessing flushing events during 6-hour submersible dives
or even for the few months' recording capability of conventional, self-powered,
bottom-moored instruments retrieved by acoustical release mechanisms.
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UNRESOLVED PROBLEMS
Many large olistoliths were seen to be resting on the seabed somehwat less
deeply submerged in the sediment than low-level radioactive waste drums. How-
ever, there is no collaborating evidence that the olistoliths arrived into the
site subsequent to the initial dumping of waste packages. The lack of appreci-
able burial of the olistoliths is puzzling, since they probably originated by
downslope avalanching either from submarine canyons or from more proximal slump
scars. It is possible, but unproven, that the olistoliths were transported by
bottom-hugging fluidized debris flows and therefore not impacted into the seabed.
The time of movement and mechanism of emplacement of various allochthonous
blocks of assorted size is intimately related to poorly-understood processes
capable of flushing the waste out of the dumpsite area to other repositories
on either the lower continental rise or abyssal plain.
Corrosion of the metal containers produces a vertical streaking of iron
oxides in the sediment at the ends of the barrels. If the containers had been
disturbed during residence on the seabed, one should expect to see generations
of streaking at different angles to the vertical. None of the audiotape
commentaries of Bruce C. Heezen made during the ALVIN dives lend insight into
this possibility (Heezen, 1975-76).
Olistoliths and remnant hills were rather commonly observed in the 2800 m
low-level radioactive waste dumpsite where a broad amphitheatre-shaped slump
scar has been mapped (Figure 15). Are the olistoliths associated with the slump
scar and were these blocks torn from place during the slumping event? Large
blocks were observed in the northwestern sector of the low-level radioactive
waste dumpsite, but neither detailed bathymetry nor side-scan sonar records
are available to reveal if slump scars are also present at shallower depths
A correlation of blocks with slump scars is important to establish since the
presence of blocks (readily visible from submersibles and bottom photographs)
is perhaps easier to detect than the slump scars. Waste containers in areas
of existing slump scars cannot be considered to be permanently deposited at
those sites. :
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A meandering, anastomosing channel was mapped where it crosses a slump
scar. The presence of the channel raises the question of whether the slope
failure of high-porosity and rapidly-deposited sediment of the channel levees
was the cause of the meandering and anastomosing nature of the channel in this
region, or whether the channel sought out an already existing slump depression
as a more optimum route into deeper water environments. Lack of detailed
bathymetry prevents estimation of the extent to which the upper continental
rise is dissected by channels. Since channels are bypass routes, waste
containers along their course are subject to movement and extensive mechanical
abrasion during brief but high-energy, turbulent flows.
Numerous submarine canyons incise the continental slope in the northern
and western portions of DWD-106. Small-scale gullies, ravines, and spurs were
conspicuous, especially during Dives 587 and 590 farthest landward on the slope.
Although present bathymetric data are insufficient to resolve details of the
morphology of these canyons and gullies, analogies to better-surveyed canyons
along the margin of New England suggest that they may display a dendritic
pattern. Such a pattern would imply a deep subaqueous process of headward
erosion. One likely causal agent for this process is bioerosion resulting
from boring and tunneling of crustaceans (mostly crabs) and bivalves feeding
on substrates containing organic carbon. Observations made during the 1975
and 1976 ALVIN diving programs do not address sufficiently the occurrence and
magnitude of contemporary bioerosion. Perhaps more diving needs to be carried
out in the axial parts of the canyon and gullies where the erosion is most
extensive due to the outcropping of pre-Pleistocene layers with carbon contents
in excess of 2%. Based on the working hypothesis that canyons are most exten-
sively carved at times of lowered sea level when shore lines are in close
proximity to canyon heads, the canyons within the dumpsite region should not
be expected to be particularly active at present. However, if bioerosion of
the type documented by Warme (1975) and Palmer (1976) and of the type which may
be pervasive in the Hudson Canyon is a major agent in slope denudation, there
is no reason to suspect that the canyons are not subject to contemporary
flushings resulting from catastrophic failure of heavily tunneled canyon and
gully walls. The very important geological question of just what is the most
significant process in sculpturing the submarine canyons off the east coast of
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the United States is still open. However, the present study provides some
insight into the processes which appear to have influenced the DWD-106 and
2800 m low-level radioactive waste disposal areas.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA 520/1-83-018
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Geologic Observations at the 2800-Meter
Radioactive Waste Disposal Site and Associated
Deepwater Dumpsite 106 (DWD-106.) in the Atlantic Ocean
5. REPORT DATE
September 1983
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
Martine Dreyfus Rawson and William B. F. Ryan
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Department of Geological Sciences
Lament-Doherty Geological Observatory
of Columbia University
Palisades, New York 10964
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
Contract No.
68-01-3933
12. SPONSORING AGENCY NAME AND ADDRESS
Office of Radiation Programs (.ANR-461)
U.S. Environmental Protection Agency
401 M St., S.W.
Washington, B.C. 20460
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
ANR-461
ABSTRACT
During 1975 and 1976 a total of eight manned submersible dives with DSRV ALVIN
were carried out in a relatively small region of the Atlantic 2800m radioactive
waste dumpsite and were centered at 38°30'N and 72°09'W. Six other dives were
distributed through the northern part of Deepwater Dumpsite 106 (DWD-106) near the
boundary of the continental rise/continental slope. One of the primary purposes of
these dives was to observe the geological conditions in this disposal region
slightly south of the Hudson submarine Canyon.
The lower continental slope was found to be incised by submarine canyons
debouching into the northern side of DWD-106. The upper continental rise was
incised by narrow meandering channels. One of these channels passed through the
radioactive waste dumpsite and was surveyed in detail.
On the upper continental rise the local terrain was relatively flat but studded
with numerous tracks, trails, holes, and mounds of biological origin. The sediment
carpet was composed of a gray silty-clay. Detailed mineralogical analysis was
performed.
Boulders and large allochthonous blocks (olistoliths) were encountered on many
of the dives. Bottom currents were detected during a majority of the dives. Scour
moats were present around rock outcrops and low-level radioactive waste containers.
These containers were observed in varying states of integrity.
On the continental rise the local terrain was partly huramocky, with relief of
the hills occasionally exceeding 20-30m. Based on this study the dumpsite areas are
considered to be in a dynamic deepsea environment.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS C. COS AT I Field/Group
ocean disposal
low-level radioactive waste disposal
marine geology
marine foraminifera
Hudson Canyon geology
packaging for ocean disposal
|18. DISTRIBUTION STATEMENT
Unlimited Release
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
61
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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