-------
Bottom Sediments
Bottom sediments of the upper Bay are predominantly
silt and clay except in the nearshore zone where sand
locally derived from coastal erosion predominates (Ryan,
1953; Schubel, 1968a; Palmer et al., 1975). Sand is also
abundant on the Susquehanna flata—an estuarine delta formed
near the head of the estuary by deposition of sand discharged
by the Susquehanna during periods of very high flow. Since
construction of the dams along the lower reaches of the
Susquehanna, very little sand, and all of that fine-grained,
is discharged into the Bay during periods of low to moderate
riverflow. Conowingo, the last of the dams to be constructed
and the one closest to the mouth of the River, was completed
in 1928. Except during periods of very high flows such as
Tropical Storm Agnes in June 1972, the only active source of
sand to the main body of the Bay is erosion of its margins.
Quartz is the dominant mineral in the silt and sand
size fractions and generally accounts for more than 90% by
mass of the total sand-silt fraction. Muscovite, glauconite,
and biogenic particles are also ubiquitous in the silt size
fraction. The most common clay minerals are illite,
kaolinite, and montmorillonite which occur roughly in the
ratios 2:1:1 (Owens et al., 1974).
A map showing the percent by mass of clay in the bottom
sediments of the main body of the upper Chesapeake Bay, in
the Patapsco estuary and in the lower Chester River estuary
is presented in Fig. 13. A map depicting the distribution
pattern of the ratio of the mass of the silt fraction to the
sand fraction in the same area is shown in Fig. 14. These
figures clearly show that the bottom of the upper Bay is
blanketed largely by mud (silt and clay), and that the mean
grain size of the bottom sediments in the Bay proper tends
to decrease downstream. Relatively little has been published
about the character of the sediments in the tributary
29
-------
76* <0' W
Fig. 13
7S«JO'
39* SO'
NORTHERN CHESAPEAKE BAY-
J9*«0'N
19*20'
3V 10'
19-CO'
J8*55'N
Map showing the percent by mass clay in the
surface sediments of upper Chesapeake Bay
(after Palmer et al. 1975).
30
-------
NORTHERN CHESAPEAKE BAY
7««40'W
Fig. 14
76'30'
75*20'
76*10'
7E-OC'
7««*o'w
Map of the ratio of silt to sand in the surface
sediments of the upper Bay (after Palmer et al.
1975) .
31
-------
estuaries to the upper Bay, other than the Patapsco and the
lower Chester. The sedimentological and geochemical
investigations being conducted by the Maryland Geological
Survey in the major tributaries will provide much needed
information.
It is well known that many contaminants—metals,
hydrocarbons, chlorinated hydrocarbons (CHCs), including
pesticides and polychlorinated biphenyls (PCBs), micro-
organisms, and oils and greases—are adsorbed to particles
and are concentrated in the finer size fractions. Since
these contaminants are scavenged relatively rapidly from the
water by fine-grained particulate matter, their dispersal
and accumulation are controlled largely by suspended sedi-
ment dispersal systems.
Turekian and Scott (1967) and Carpenter et al. (1975)
reported on the introduction of metals to the upper Bay by
the Susquehanna. There have been few published studies
documenting the levels of metals or other contaminants in
the bottom sediments of the upper Chesapeake Bay and its
tributary estuaries, except in Baltimore Harbor, and fewer
still of the processes that control the occurrence and the
distribution of these contaminants in time and space, and
their availability for uptake by organisms.
Sediments within Baltimore Harbor are enriched in most
metals with concentrations 3 to 50 times those found in
sediments of similar texture along the axis of the main
body of the Bay (Villa and Johnson, 1974). Chromium, copper
and lead values in the Harbor averaged 20, 50 and 13 times
the corresponding values in the Bay proper. Cadmium was
approximately six times higher in the Harbor than in the Bay.
Of all metals analyzed, only manganese had approximately
equal concentrations in the two areas. The distribution of
metals within the Harbor, as shown by Villa and Johnson's
(1974) analyses of samples from 176 stations, generally
reflected the industrial inputs. Their report points out
32
-------
"all Harbor metals investigated by manganese were 3 to 50
times greater than their Bay counterparts. These factors
should be carefully weighed when considering the disposal of
dredged spoil in any open Bay areas."
Tsai et al. (1979) have recently conducted a bioassay
analysis of Baltimore Harbor sediments. Their results
showed that the toxicity of these sediments to the test
organism, fish (mumichogs and spot), varied with location
in the harbor and was roughly proportional to the metals
concentrations in the sediment. In general sediments of the
inner harbor were rated moderately toxic with highly toxic
sediment in the marginal creeks. Outer harbor sediment was
rated low in toxicity.
High metal concentrations in sediment are not in them-
selves diagnostic indicators of the potential effects of
"pollution" unless all the metals present in sediment are
available for biological uptake. The methods of extraction
of metals from the sediments for chemical analyses used in
Villa and Johnson's (1974) study do not give a reliable
indication of the available fraction; that fraction available
for biological uptake, or that might be mobilized during
dredging and disposal.
Munson (1975) documented the distributions of total
PCBs and DDTR (the total residual of the pesticide DDT) in
the surficial sediments of the main body of the upper
Chesapeake Bay and the Patapsco estuary. His analyses
showed "that the sediments of Baltimore Harbor are quite high
in PCB compared with the rest of the bay, except the station
at the mouth of the Gunpowder River." The highest values
of DDTR were also found in Baltimore Harbor and the mouth
of the Gunpowder although the range in values was much more
restricted.
While there are relatively few observations of con-
taminant levels in the surfacial sediments of the upper Bay,
analyses of the longer-term sedimentary record are even more
33
-------
scarce. Schubel (1972a) reported on the distribution of
extractable iron and zinc in a 165 cm long core taken in the
upper Chesapeake Bay off Howell Point. The core was sampled
at the surface and at 20 cm increments to the bottom of the
core. One might have anticipated that the concentrations of
iron and zinc would decrease with depth, since man's impact
has presumably increased in recent decades. The results
showed, however, that below the surficial layer the concen-
trations were nearly uniform with depth. The concentration
of zinc was about 70 ppm (dry weight) and the concentration
of iron about 20 ppt (dry weight).
Other more recent data from the central Bay (Schubel
and Hirschberg, 1977; Goldberg et al., 1978) show that the
vertical distribution of metals over the top meter of sedi-
ment are quite variable. Some cores show strong decreasing
downward gradients in metal concentrations while others are
more uniform. Some of this variability may be the result
of the activities of burrowing organisms, which are hetero-
geneously distributed.
The Susquehanna River is probably the major source of
sediment to the main body of the Chesapeake Bay at least as
far seaward as the mouth of the Patapsco, and to the lower
reaches of the estuaries that are tributary to this segment
of the Bay. Near the head of the Bay—from Tolchester to
Turkey Point—the sedimentation is completely dominated by
the Susquehanna River (Schubel, 1968a,b, 1971a, 1972a,b).
Sedimentation Rates
Sediment deposition rates in the Chesapeake Bay are
not well known. Most published estimates of contemporary
and recent sedimentation rates are based on simple sediment
budget models in which the sedimentation rate was the calcu-
lated term required to balance the budget. Using such a
model Schubel (1968a) estimated that during years of average
riverflow the sedimentation rate in the upper reaches of the
34
-------
Bay from Tolchester to Turkey Point averaged about
2 to 3 mm/yr. Using a similar model for approximately this
same segment of the Bay, Biggs (1970) estimated a mean sedi-
mentation rate of 4 mm/yr. Schubel (1971a, 1976) has at
various times estimated mean sedimentation rates of
1 to 2 mm/yr for the middle reaches of the Bay, and Biggs
1970) estimated it at about 1 mm/yr.
Recently, Schubel and Hirschberg (1977) and Hirschberg
and Schubel (1979) reported radiometrically-determined
contemporary sedimentation rates for the Chesapeake Bay.
For a core from a station off Tilghman Island (38°41'30"N,
210
76°24'00"W) using the Pb dating method, -they estimated
a mean sedimentation rate of between 1 to 1.5 mm/yr for the
past century or so. For a core from the upper bay, near
the mouth of the Sassafras River, they report a "normal"
sedimentation rate of 5 mm/yr. They note, however, that
sedimentation in this region is strongly dominated by
episodic floods, and that the true long-term sedimentation
rate is probably twice this value.
210
Goldberg et al. (1978) also reported Pb measurements
for Chesapeake Bay sediments. Their calculated sedimentation
rates appear to us to be anomalously high. We suspect their
cores were disturbed by burrowing organisms which destroyed
their chronology. George Helz (Personal Communication, 1980)
and O.M. Bricker (Personal Communication, 1980) have also
210
dated cores from the Chesapeake Bay using Pb but their
results have not been published.
Average sedimentation rates estimated from sediment
budgets from "typical" years are relatively meaningless in
the upper reaches of the Bay—above Tolchester. The
geological record of this part of the estuarine system is
dominated by floods. During Tropical Storm Agnes (June,
1972), Schubel and Zabawa (1978) and Zabawa and Schubel
(1974) estimated that the sediment discharged would, if
spread uniformly over the area between Tolchester and
35
-------
Turkey Point, form a layer about 18 cm thick. Cores taken
throughout this area showed accumulations of from 10 to 30 cm
outside of the channel. Long stretches of the channel shoaled
by more than 1 m. The deposit of at least one other large
flood, that of March 1936, appears also to have been preserved
in the sedimentary deposits of the upper Bay.
Sediment accumulation rates in channels are greater than
the rates in shallower areas on the sides. The shoaling rate
of the Chesapeake and Delaware Canal Approach Channel can be
estimated by dividing the average volume of material that
would have to be removed to maintain the Channel at its
project depth by the area of the Channel and by the period of
time between successive dredgings. The Approach Channel is
approximately 52.8 km in length with an average width of
2
137 m, so it has an area of approximately 5.7 million m .
Maintenance dredging in this channel averages 0.9 million
>nl
3
3 3
m /yr (1.2 million yd /yr). The average rate of sediment
accumulation in the channel is then about 0.9 million m"
2
+ 5.7 million m = 15 cm/yr.
Farther seaward in the Bay, the sedimentation rate
decreases substantially, but the actual value is not well
known. In the main body of the Bay between Swan Point and
the Maryland-Virginia line, the average sedimentation rate
away from the littoral (nearshore) zone and outside of
dredged channels is probably between 1 to 3 mm/yr with the
higher rate being representative of the northern reaches of
this segment.
The annual shoaling rate for the Approach Channels to
Baltimore Harbor can be estimated by dividing the amount of
material that must be dredged annually to maintain the
Craighill and Brewerton Extension Channels, 1.5 million m
(% 2 million yd ), by the area of these channels, 6.7 million
2 2
m ( 8 million yd ). This method yields a shoaling rate of
about 23 cm/yr.
36
-------
Effects of a Major1 Event--Agnes
Distributions described previously are "typical" of
"average" conditions in Chesapeake Bay. But in addition to
these "normal" variations, marked fluctuations can result
from catastrophic events such as floods and hurricanes.
There was, until Tropical Storm Agnes in 1972, a dearth of
direct observations of "rare" events on the distribution of
suspended sediment not only in Chesapeake Bay, but in the
entire coastal environment.
Tropical Storm Agnes presented scientists with an
unusual opportunity to document the impact of a major storm
on a major estuarine system. There was little wind associated
with Agnes when she reached the Bay area, but torrential rains
sent riverflows of the major tributaries to record or near-
record levels. Heavy rains stripped large quantities of
soil from throughout most of the drainage basin, and flooding
rivers carried significant quantities of sediment into
Chesapeake Bay.
Nineteen seventy-two started out not very unlike most
years, although it was somewhat wetter. During the spring
freshet in March, flow of the Susquehanna was fairly high,
exceeding 8900 m /sec, and the concentration of suspended
sediment in the "mouth" of the River (Conowingo) on one day
reached 190 mg/&. Between 1 January 1972 and 21 June 1972
the concentration of suspended sediment at Conowingo exceeded
100 mg/£ on only four days—not unlike most years. During
May and the first 20 days of June of 1972, the concentration
was generally between 10-25 mg/£; somewhat higher than average
for that time of year, but not really "abnormal." Then Agnes
entered the area and torrential rains fell throughout most
of the drainage basin of the Susquehanna producing record
flooding. The day the Susquehanna crested, 24 June 1972,
the average daily flow at Conowingo exceeded 27,750 m /sec—
the highest average daily flow ever recorded—exceeding the
37
-------
previous daily high by about 33 percent. The instantaneous
peak flow on 24 June of more than 32,000 m /sec was the
highest instantaneous flow ever reported over the 185 years
of record. The monthly average discharge of the Susquehanna
of about 5100 m /sec for June 1972 was the highest average
discharge for any month over the past 185 years, and was more
than nine times the average June discharge over the same
period. Comparison of the monthly average discharge of the
Susquehanna during 1972 with the ensemble monthly average
over the period 1929-1966 clearly shows the departure of the
1972 June flow from the long-term average June flow, Fig. 15.
Even before Agnes, 1972 had been a "wet" year. Salini-
ties throughout much of the Bay were lower than their more
normal values. With the large influx of fresh water following
Agnes, salinities fell sharply. The lag between time of
maximum discharge and the time of minimum salinity varied,
of course, with location and depth. In the surface layers
of the upper 180 km of the estuary the salinities reached
minimum values within 2 to 5 days of the cresting of the
Susquehanna. In the near-bottom waters in the same region,
minimum salinities were not reached in some areas until
14-15 July 1972, 20 days after cresting. The tidal reaches
of the Susquehanna were pushed seaward more than 80 km from
the mouth of the river at Havre de Grace, that is, nearly to
the Chesapeake Bay bridge at Annapolis, Maryland. The front,
separating the fresh river water from the salty estuarine
water, was more than 35 km farther seaward than ever previously
reported, Fig. 16.
Reestablishment of the "normal" salinity distribution
is effected by the flow of more saline waters up the estuary
in the lower layer and subsequent slow vertical mixing of the
lower and upper layers. The combination of large fresh water
inputs accompanying Agnes and the compensating upstream flow
of salty water in the lower layer produced vertical salinity
gradients larger than any previously recorded throughout much
38
-------
ouuu
5000
4000
_
'« 3000
•9
to
E 2000
1000
0
,
L ,
I
Ensemble Monthly Average 1929-1966 "
.
•
-
• — -
i '
I !
200,000
1 60,000
1 40,000 -
1
o
120,000 8
1 00,000 'c
80,000
6O,OOO
40,000
2O,000
0
JAN FEB MAR APf? MAY JUN JUL AUG SEP OCT NOV DEC
Fig. 15 Susquehanna River flow at Conowingo (MD),
ensemble average by month for the period
1929-1966, and the monthly average flow
during 1972.
39
-------
Turkey Pt '
is no
Tolchester
ISO 2F
3ZTA
3ZIA
858 C
SALINITY
26 JUNE 1972
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85
DISTANCE FROM MOUTH OF SUSQUEHANNA RIVER (HAVRE DE GRACE) IN KILOMETERS
Fig. 16 Longitudinal distribution of salinity in upper
Bay on 26 June 1972, two days after the
Susquehanna crested at Conowingo (MD) follow-
ing passage of Tropical Storm Agnes.
40
-------
of the Chesapeake Bay estuarine system. Abnormally large
vertical gradients persisted throughout the summer. Even in
early autumn the vertical salinity gradients were more typical
of spring conditions that those characteristic of the fall
season.
The flooding Susquehanna dumped a large mass of sediment
into the upper Bay. On 22 June 1972 when riverflow increased
rapidly as a result of heavy rains the concentration of
suspended sediment at Conowingo reached 400 mg/£. On 23 June
1972, riverflow exceeded 24,400 m /sec, and the concentration
of suspended sediment jumped to more than 10,000 mg/£,—a con-
centration more than 40 times greater than any previously
reported for the lower Susquehanna. On the 24th of June, no
sample was collected because the dam was evacuated for safety
reasons. By 25 June, riverflow had decreased to about
23,100 m /sec, and the concentration of suspended sediment
to about 1,450 mg/£. On 30 June, riverflow was 4,600 m /sec,
and the concentration of suspended sediment, 70 mg/£, Figs. 17
and 18.
During the ten-day period, 20-30 June 1972, the
Susquehanna River probably discharged more than 31 million
metric tons of suspended sediment into the upper Chesapeake
Bay (Schubel, 1972) . This is more than 25 times its sediment
discharge of the previous year. In most years the Susquehanna
probably discharges between 0.5 to 1.0 million metric tons of
suspended sediment into the upper Bay (Schubel, 1968a, 1972b;
Biggs, 1970). The bulk of the sediment discharged during
Agnes was silt and clay; the remainder was fine sand.
The sediment-laden floodwater produced anomalously high
concentrations of suspended sediment throughout much of the
Chesapeake Bay estuarine system. In the main body of the
Bay, the effects were, of course, most dramatic in the upper
Bay. The distribution of suspended sediment along the axis
of the upper Bay on 26 June 1972, two days after the
Susquehanna crested at Conowingo, is plotted in Fig. 19. The
figure shows that the concentration of suspended sediment at
41
-------
280
270
260
250
240
230
220
210
200
190
1 30
170
-
— cni
«
" 150
rO
t 140
CM
0 130
x 120
! 10
100
90
so
o w
70
60
50
40
30
20
10
0
-
-
-
-
.
-
_
-
-
_
-
-
A '
1 1 1 1 1 1 1 1 1 M
JAN ' FEB
n
\ (A
V J \
V v J
! ! ! ; | ill
)
k
1
-
-
-
1 UUU
975
950
925
A 900
- 875
-
. -
-
-
-
-
-
-
-
-
-
-
-
850
825
800
^75
750
725
700
675
650
625
500
575
550
-j 525
-J 500
-I 475
1
- 425
-
—
-
1 -
-
1 '< \ r
I I
\ Jl
i IV-
1 i\
\ Jv V H 1 \ t !
\ f 1 I 1 \
J ^ u J y | / \l y ^ _
'i MM: iii i i i i i ' MjW\r\A /r\lA/T\iVj/nAW/Kini M i i i i I i M
MAR APR MAY JUN JUL ' AUG ' SEP ' OCT ' MOV ' DEC
400
375
350
325
300
275
250
225
200
1 75
1 50
125
100
75
50
25
0
972
Fig. 17 Discharge of Susquehanna River at Conowingo
(MD) during 1972.
42
-------
1 1 IJUU
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
•ss
400
390
380
370
360
350
340
330
320
31 0
300
290
280
270
260
- 250
o. 240
E 230
220
210
200
1 90
80
1 70
1 60
50
40
30
20
1 0
00
90
80
70
60
50
40
30
20
10
n
•
-
-
-
-
-
-
-
-
-
s?
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
"
-
-
-
-
-
-
-
-
-
-
-
-
-
-
1
I p
kj^W y
TWirTffli i rf
1 M i 1 1 1 1 1
,
~
i
1 J
%*\J
ii 4 1 1 1
i 1 1 U i 1 1 1 1 i
1
JLi 1
*• *sf^ ^
1 1 1 1 1 III
j u 1 i i i 1 1 1 1 i i < M i i i i i i i i i i i i 1 1 i !
-
-
-
-
-
-
-
-
-
-&
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
i 1 "
i \\i> ii ~
i in, n ~
1 i il ! \ n
M^J\Li _>&p» ii. i* ^ \Jj
i i 1 1 ?TI i 1 1 HM 1 f i fri r rMft in Mill
1 1 UUJ
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
~ 400
390
380
370
360
350
340
330
320
310
300
290
280
270
260
250
240
230
220
210
200
1 90
80
70
60
50
40
30
20
I 0
00
90
80
70
60
50
40
30
20
10
n
01
1972
Fig. 18
Concentration of suspended sediment (mg/z) in
the Susquehanna River at Conowingo (MD) during
1972.
43
-------
the surface dropped from more than 700 mg/£ off Turkey Point
(Station 927SS) at the head of the Bay to about 400 mg/£ at
Tolchester (Station 913R, 30 km farther seaward), and to
approximately 175 ing/2, near the Bay Bridge at Annapolis
(Station 858C). The concentrations of suspended sediment
at mid-depth in the upper reaches of this segment of the Bay
showed a similar distribution pattern although the concentra-
tions were generally greater than near the surface. Seaward
of Station 903A, however, there was an abrupt decrease in
the concentration of suspended sediment below about 10 m.
This distribution resulted from the over-riding of the
relatively "clean" estuary water by the sediment-laden
Susquehanna River water.
The marked downstream decrease in the concentration of
suspended sediment in the upper Bay resulted almost entirely
from the removal of the material by settling; there was
little dilution of the Susquehanna inflow by the Bay water
in this segment of the Bay. Riverflow was so great that the
tidal reaches of the Susquehanna were pushed seaward nearly
to the bridge at Annapolis—more than 35 km farther seaward
than ever previously reported.
By 29 June 1972 the concentrations of suspended sediment
had decreased significantly throughout the upper Bay. Maxi-
mum concentrations at that time were observed between
Stations 917S and 909, and did not exceed 300 mg/£. The
concentration of suspended sediment decreased both upstream
and downstream of this approximately 20 km long legment. The
longitudinal gradient of suspended sediment that had charac-
terized the upper Bay on 26 and 27 June had disappeared.
Longitudinal distributions of total suspended solids in the
upper Bay during the week following Agnes show that the
concentrations dropped quickly following peak discharge, and
that the bulk of the material discharged into the main body
of the Bay at Turkey Point was deposited above Station 903A.
Concentrations of suspended solids were relatively high,
however, over all of the Maryland portion of the Bay proper.
44
-------
Turkey Pt.
ois
Tolchester
no me ED IZF HA • IIEA
858 C
4
8
en 12
ac
H 16
UJ
?20
x 24
i—
Q
32
36
40
TOTAL SUSPENDED SOLIDS mg/l
26 JUNE 1972
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85
DISTANCE FROM MOUTH OF SUSQUEHANNA RIVER (HAVRE DE GRACE) IN KILOMETERS
Fig. 19 Longitudinal distribution of suspended sediment
(mg/£) along the axis of the upper Bay on
26 June 1972, two days after the Susquehanna
nested at Conowingo (MD) following passage of
Tropical Storm Agnes.
45
-------
and the concentrations of total suspended solids remained
i
anamalously high throughout most of the upper Bay for more
than a month.
As the normal two-layered circulation pattern was re-
established throughout the upper reaches of the Bay, there
was a net upstream movement of sediment suspended in the
lower layer. Sediment previously carried downstream and
deposited by the flooding Agnes waters was resuspended by
tidal currents and gradually transported back up the estuary.
The routes of sediment dispersal are clear, but the rates of
movement are obscure. The data do not permit reliable
estimates of the rates of sediment transport, particularly
during the recovery period.
Comparison of post-Agnes data from the middle and lower
reaches of the Bay with data from more "normal" years indi-
cates that throughout most of the summer, concentrations of
suspended sediment were 2 to 3 times higher than average for
that time of year. Seaward of Station 858C—just south of
the Bay bridge at Annapolis—concentrations in July and
August 1972 did not exceed 10 mg/£ except near the bottom.
Summary
During the spring freshet and other occasional short
periods of very high riverflow, the upper reaches of the
Chesapeake Bay behave like the tidal reaches of a river.
The Susquehanna overpowers the characteristic net non-tidal
estuarine circulation and the net flow and sediment trans-
port are seaward at all depths. The transition from river
to estuary, sometimes as far as 40 to 45 km seaward of the
mouth of the Susquehanna at Havre de Grace, is characterized
by a front separating the fresh river water from the saline
estuary water. Generally, most of each year's supply of new
fluvial sediment is discharged during the freshet. The bulk
of this is deposited in the upper Bay north of Tolchester.
The spring freshet, then, is a period of fluvial domination
46
-------
of the upper bay and of its suspended sediment population and
is characterized by a close link between the suspended sedi-
ment population and the principal "ultimate" source of
sediment—the Susquehanna River.
With subsiding riverflow, the characteristic net non-
tidal estuarine circulation is reestablished in the upper
reaches of the Bay. The concentrations of suspended sedi-
ment are greater than those either farther upstream in the
source river or farther seaward in the estuary. This zone
of high suspended sediment concentration, the "turbidity
maximum," is produced and maintained by the periodic resus-
pension of bottom sediment by tidal scour and by the
sediment trap produced by the net non-tidal circulation.
The passage of tropical storm Agnes in June 1972
resulted in record flooding throughout the drainage basin of
the northern Chesapeake Bay. On June 24, the day the
Susquehanna crested at its mouth, the instantaneous peak flow
exceeded 32,000 m /sec. The daily average discharge of
27,750 m /sec for that day exceeded the previous daily average
high by nearly 33 percent. Throughout the bay, salinities
were reduced to levels lower than any previously observed.
On 26 June 1972, salinities were less than 0.5 °/oo from
surface to bottom throughout the upper 60 km of the bay and
the surface salinity was less than 1 °/oo in the upper 125 km
but had nearly recovered to normal levels by September.
On June 24, the concentration of suspended sediment in
the mouth of the Susquehanna exceeded 10,000 mg/H and in a
one-week period the sediment discharge exceeded that of the
past several decades. The bulk of this was deposited in the
upper 40 km of the Bay.
47
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CASE STUDY 1
THE ANALYSIS
Our first case study was for the Chesapeake and Delaware
Canal Approach Channel, Fig. 20. We considered two disposal
options: overboard adjacent to the Channel, and in the deep
trough south of the Bay Bridge at Annapolis.
Principal Findings, Conclusions and Recommendations
1. Most of the sediment accumulating in Chesapeake
and Delaware Approach Channel and in contiguous areas
comes from erosion of the drainage basin of the
Susquehanna River.
2. The sediments in the Chesapeake and Delaware
Approach Channel are not measurably different in their
physical and chemical characteristics and in their
contaminant levels from those accumulating in areas
contiguous to the channel or in the deep trough.
3. Upper Chesapeake Bay normally experiences rapid
sediment deposition and high turbidity because of sus-
pended sediment and phytoplankton growth. Processes
controlling these normal background conditions must be
considered in planning, executing, and regulating dredg-
ing and disposal operations.
4. Naturally-deposited sediments and dredged
materials are resuspended and dispersed in the upper Bay
by tidal currents, turbulence due to wind waves and
ship wakes, flood-induced currents, and the long-term
estuarine circulation. These processes are most
effective in shallow waters and least affective in the
deep trough of the central Bay.
5. Sediment-associated metals in dredged materials
of the upper Bay do not pose a problem to benthic organ-
isms or to the overlying water column, during or
subsequent to disposal operations.
48
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6. Sediment-associated organic compounds, such as
chlorinated hydrocarbons, deserve particular attention
because of high toxicity at low concentrations, signifi-
cant potential for release from sediment, public concern
and the scarcity of data.
7. Physical and chemical effects of the discharge
plume from dredging and disposal operations are normally
small and have no long-term effects on organisms or
environmental quality.
8. Depletion of dissolved oxygen by dredging and
disposal is a local, transitory phenomenon in shallow
waters, and is unlikely to have a measurable effect on
dissolved oxygen levels in near-bottom waters in the
trough south of the Bay Bridge.
9. Benthic communities in subaqueous dredged mate-
rial disposal sites recover to near normal abundances
within one to two years. Community diversity may take
somewhat longer to recover to pre-disposal levels.
Recovery of benthic abundance and diversity is expected
to be quicker in the deep trough in the central Bay than
in shallow waters of the upper Bay.
10. Containment of dredged materials or utilization
of disposal sites far from the channels can be expected
to decrease the frequency of dredging required to main-
tain the Chesapeake and Delaware Canal Approach Channel.
11. The deep trough in the central Bay appears to
be an attractive site for disposal of uncontaminated
sediments. There are, however, several questions that
should be answered before the trough is considered as
a disposal site.
a. To what extent is the trough used by over-
wintering fish? At what levels in the water
column do they congregate and in what concen-
trations?
b. To what extent is the trough used by blue crabs
as an over-wintering area? What parts of the
49
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trough do they utilize?
c. To what extent would disposal in the trough alter
its characteristic properties?
50
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CASE STUDY 1. CHESAPEAKE AND DELAWARE
CANAL APPROACH CHANNEL
The first case study we made was for material dredged
from the Chesapeake and Delaware Canal Approach Channel,
Fig. 20. The Chesapeake and Delaware Canal Approach Channel
extends from approximately Pooles Island northward to the
western end of the Canal.
The Chesapeake and Delaware Canal Approach Channel is
shown in Fig. 20. The rationale for the steps we followed
in assessing dredging/disposal options for this project are
given in Schubel et al. (1979). The steps are shown sche-
matically in Fig. 2.
Step I. Water Quality Certificate
Since the C & D Approach Channel is an authorized U.S.
Army Corps project, it requires only a Water Quality Certi-
ficate. Under Section 10 of the Rivers and Harbors Act of
1899 (33 U.S.C. S401 et. seq.) the U.S. Army Corps of
Engineers is charged with the responsibility of evaluating
requests to make physical alterations in the navigable
waters of the United States. A dredging operation is such
a physical alteration. The District Office serves as a
clearing house for other Federal, State, and local agencies
concerning the environmental effects of a proposed action.
The primary Federal agencies reviewing applications for
physical alterations to areas under the aegis of the
Baltimore District are the U.S. Environmental Protection
Agency, the U.S. Fish and Wildlife Service of the Depart-
ment of the Interior, and the National Marine Fisheries
Service of the Department of Commerce.
The decision to issue a Water Quality Certificate is
based on an evaluation of the probable impact of the proposed
activity on the public interest. That decision should reflect
the national concern for both protection and utilization of
51
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Fig. 20 Map showiiag the approach channel to the
Chesapeake and Delaware Canal.
52
-------
important resources. The benefit which reasonably may be
expected to accrue from the proposal must be balanced against
its reasonable forseeable detriments. All factors which may
be relevant to the proposal are to be considered; among
those are conservation, economics, anesthetics, general
environmental concerns, historic values, flood damage pre-
vention, land use classification, navigation, recreation,
water supply, water quality, and in general, the needs and
welfare of the people. No permit will be granted unless
its issuance is found to be in the public interest.
Step II. Characterization of Material to be Dredged
The State of Maryland requires that certain tests be
made to characterize materials proposed for dredging and
to characterize materials in the proposed disposal area.
These tests are listed in Table 1 which also indicates
which of the tests have been conducted for sediments in the
Chesapeake and Delaware Approach Channel and in the two
disposal areas we selected for analysis. Characteristics
of the materials accumulating in the Chesapeake and Delaware
Canal Approach Channel and in these two disposal areas are
summarized in Table 2.
Step III. Identification of Potential
Dredging/Disposal Options
We evaluated two dredging/disposal options: (1) hydrau-
lic dredging and overboard pipeline disposal in the area
adjacent to the channel, and (2) bucket and scow dredging
with disposal by hopper barge in the deep trough south of
the Bay Bridge at Annapolis. Another alternative that might
be considered is the filling of marginal areas. In the past
a large fraction of the material dredged from the C & D
Approach Channel has been placed in Pearce Creek. The
availability of data for comparative tests of sediments in
53
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the two potential disposal sites is summarized in Table 1;
the data themselves are summarized in Table 2. Important
characteristic properties of each of these two potential
disposal areas are summarized in Table 3. The data
recorded are typical values.
Step IV. Assessment of Potential
Dredging/Disposal Options
The short-term and long term environmental and ecologi-
cal effects of the two dredging/disposal options we
considered are summarized in Table 4. We did not attempt
to evaluate the socio-economic factors (Step IVc, Fig. 2).
With respect to environmental and ecological effects
during disposal, there is little to choose between the two
disposal alternatives. The effects of overboard disposal in
the upper Bay on the water column and on organisms living in
the water column are local in time and space, and negligible
(Table 4 and references). Studies in many other areas
throughout the world indicate clearly that if this same
material from the Approach Channel were dumped in the trough,
water-column effects during disposal would also be local in
time and space, and negligible (Table 4 and references). In
both areas, disposal would result in the immediate burial of
most of the benthic organisms. The trough has fewer bottom-
dwelling organisms than the area in the upper Bay adjacent
to the Channel. The only potential ecological effect during
disposal we identified which we could not assess with exist-
ing data was the uptake of chlorinated hydrocarbons (CHCs)
by plankton, benthos, and nekton.
The potential environmental and ecological effects
subsequent to disposal in the two environments are of greater
concern because of their greater uncertainty. The principal
problems are not with the metals as is commonly supposed.
All available evidence indicates that metals in dredged
materials do not pose a significant threat to the environment,
54
-------
to the biota, or to human health if the materials are kept
in a geochemical environment similar to that from which
they were dredged. According to Turekian (1974) "The best-
informed conclusion must be that, as far as metals are
concerned, what has been deposited with the dredge spoil
has little chance of leaching out of the sediment. The
problems of polluted dredge spoil dumping are thus more
concerned with mobilized toxic organic compounds and changes
.in the physical character of the substrate than with the
potentially toxic heavy metals."
Since metals and other contaminants may be taken up by
benthic animals, particularly by those that burrow into the
sediment, appropriate choice of disposal areas can minimize
any potential problems. A disposal area should be selected
which minimizes the number of benthic animals that are
harvested directly from the disposal area, and which mini-
mizes the number of benthic animals that serve as food for
animals that are harvested from that area or from other
areas of the Bay.
Conclusions and Recommendations
On the basis of existing data on the environmental and
ecological effects of the two alternatives, we rank disposal
in the trough as being environmentally and ecologically .
somewhat more acceptable than disposal overboard adjacent to
the channel. Neither alternative appears to have any
unacceptable short-term or long-term environmental or
ecological effects.
The principal advantages of disposal in the deep trough
south of the Bay Bridge at Annapolis over disposal in the
area adjacent to the Chesapeake and Delaware Approach
Channel are:
(1) Disposal in the trough eliminates any possible
return of the dredged material to the Chesapeake and Delaware
Canal Approach Channel, and therefore decreases the frequency
55
-------
of dredging required to maintain the Channel. With over-
board disposal in the area adjacent to the Channel, much
of the material returns to the Channel.
(2) Any mobilization of contaminants to the water
column during disposal would be reduced with disposal in
the trough because bucket and scow dredging and disposal
operations require less water, and produce less agitation
that hydraulic pipeline operations. Even if the material
were dredged hydraulically and disposed of by scow, dilu-
tion of the dredged material by water would be less than
that required for a pipeline operation.
(3) Any mobilization of contaminants to the water
column subsequent to disposal would be reduced because of
the substantial reduction in reworking of the material by
waves, tidal currents, and burrowing organisms.
(4) Any uptake of contaminants by organisms from the
dredged material subsequent to disposal would be reduced
because of the low density of burrowing organisms and the
nearly complete mortality of this population brought on
each summer by the naturally occurring anoxic conditions of
the near-bottom waters.
(5) Changes in bottom topography by disposal in the
trough would have a much smaller impact on circulation and
other dynamic characteristics than disposal in the upper Bay.
These effects in both areas are small, but objections have
been raised by drift-net fishermen in the upper Bay.
The trough appears to be an attractive area for dis-
posal of uncontaminated dredged materials. There are,
however, a number of questions that should be answered
before any disposal occurs. These include:
(1) What are the distributions of over-wintering blue
crabs in the trough in space and in time?
(2) Would disposal of dredged materials substantially
increase the mortality of these crabs?
(.3) What are the distributions of over-wintering fin-
fish in the trough in space and in time?
56
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(4) Would disposal of dredged materials from scows
disturb these populations of over-wintering fish?
If the deep trough south of the Bay Bridge at Annapolis
were to be designated as a disposal area for material
dredged from the Chesapeake and Delaware Canal Approach
Channel, the approved period for dredging, the "dredging
window" for this Channel might have to be adjusted.
57
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Table 1. Comparative tests required by State of Maryland's
Department of Natural Resources for materials
proposed for dredging and for materials in pro-
posed disposal areas. An X in the Table indicates
that published data exist.
Parameter
C & D
Approach
Channel
X
Volatile Solids
Chemical Oxygen Demand
Hexane Extractables X
Total Organic Carbon X
Zinc
Mercury
Cadmium X
Copper X
Chromium X
Lead X
Total Keldjahl Nitrogen X
Total Phosphorous X
Chlorinated Hydrocarbons X
Particle Size X
Overboard
Area Adjacent
Channel Trough
X X
X X
X X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
58
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Table 2.
Characteristics of sediments accumulating in the
Chesapeake and Delaware Approach Channel and in
two potential disposal areas—the area adjacent
to the channel and the deep trough south of the
Bay Bridge at Annapolis.
Property
Silver
Cobalt
*Chromium
*Copper
Gallium
Nickel
*Lead
Strontium
Vanadium
Zirconium
*Zinc
*Mercury
*Cadmium
*BHC
*Chlordane
*Dieldrin
*DDT
*PCB
*Kepone
Material to
be Dredged
Area Adjacent
to Channel
Trough South of
Bay Bridget
Concentrations in PPM
117
460
80
54
106
240
270
102
302
0
0
0
0
2
± 40
± 110
± 24
± 9
± 37
± 26
± 72
± 20
± 115
—
—
.002
.009
ND
.020
.9
ND
<1
150 ± 52
455 ± 90
85 ± 26
53 ± 16
112 ± 25
225 ± 63
213 ± 44
103 ± 25
328 ± 96
128
0.9
0.001
0.005
ND
0.016
0.19
ND
Dry Mass
0.7
(12)
(25) (90) (85)
(20) (24) (12)
— — —
(26) (43) (43)
(27) (33) (34)
— — —
74
— — —
— — --
— — —
— — —
__ — —
— __ —
— __ —
— __ —
__ _— — —
59
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Property
Table 2. (continued)
Material to
be Dredged
Area Adjacent
to Channel
Trough South of
Bay Bridget
Physical Properties, Percent Mass
Water Content
*Volatile Solids
Montmorillonite
Kaolinite
Chlorite
Illite
*Sand
*Silt
*Clay
*Carbon
*Nitrogen
*Phosphorus
*0xygen Demand
Initial
Final
Oils and Greases
61.9
10.9
10
20-30
10
40
15
71.5
13.4
4%
0.2%
0.7%
56.4
10.8
10
20-30
10
40
15
71.5
13.4
3.9%
0.2%
__
66.8
8.4
Trace
10
20
50-60
19.3
55.0
25.7
1.3%
0.2%
—
300
90
g/m sed
g/m sed
1%
t Data from three sources; values have not been averaged
because different analytical techniques were used.
* State of Maryland required test.
— Data not available.
ND Not detected.
60
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Table 2, Sources of Information
1. Metals, CHCs, oxygen demand, volatile solids, oils
and greases, and phosphorous data for C & D Approach Channel
and overboard area.
Gross, M.G., W.R. Taylor, R.C. Whaley, E. Hartwig
and W.B. Cronin. 1976. Environmental effects
of dredging and dredged material disposal,
approaches to Chesapeake and Delaware Canal,
northern Chesapeake Bay. Chesapeake Bay Insti-
tute, The Johns Hopkins University, Open File
Rept. 6, 87pp.
2. Metals, carbon, nitrogen, volatile solids, and water
content data for the trough south of the Bay Bridge at
Annapolis.
Helz, G.R. 1976. Trace element inventory for
the northern Chesapeake Bay with emphasis on
the influence of man. Geochem. Cosmochem. Acta
40:573-580.
Goldberg, E.D., V. Hodge, M. Koide, J. Griffin,
E. Gamble, O.P. Bricker, G. Matisoff, G.R. Holdren,
and R. Braun. 1978. A pollution history of
Chesapeake Bay. Geochem. Cosmochem. Acta
42:1413-1425.
Schubel, J.R. and D.J. Hirschberg. 1977. 210Pb-
determined sedimentation rate and accumulation of
metals at a station in Chesapeake Bay. Ches. Sci.
18:379-383.
3. Clay mineral data.
Hathaway, J.C. 1972. Regional clay mineral facies
in estuaries and continental margin of the United
States East Coast. Pages 293-317 in B.W. Nelson,
ed., Environmental Framework of Coastal Plain
Estuaries. Geological Society of America Mem. 133.
61
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4. Sediment grain size data.
Ryan, J.D. 1953. The sediments of Chesapeake Bay.
Maryland Department of Geology, Mines, and Water
Resources, Bull. 12, 120pp.
62
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Table 3.
Characteristic properties of the two alternative
disposal sites. The values presented are con-
sidered typical.
Disposal Site
Property
Area
Adjacent
To Channel
Trough
South of
Bay Bridge
Distance from Dredging
Activity
Type of Dredging
Type of Disposal
Depth of Disposal Area
Dissolved Oxygen of
Near Bottom Waters
Salinity of Near
Bottom Waters
Temperature of Hear
Bottom Waters
1-3 km
50 km
Summer
Winter
Summer
Winter
Summer
Winter
Hydraulic
Pipeline
4 m
5-6 mSL/S.
9 mH/a
7%
6%
25 °C
2.5°C
Bucket
Scow
30 m
1 mH/H
1 mH/a
20%
19%
24°C
3.5°C
Turbulence
(A)
Amount of Sediment
Resuspension' '
Depth of Euphotic Summer
Zone Winter
Abundance of Benthic
Organisms
Importance of Area to
Fish
Spawning & nursery
Over-wintering
Frequency of maintenance
dredging required(O
High
Large
1.0 m
0.7 m
High
High
Negligible
Unchanged
Low
Small
2.0 m
5.0m
Low
Low
High
Decreased
See Appendices at end of report for documentation.
63
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Table 4. Environmental and ecological effects
of disposal alternatives.
a. Environmental effects during
disposal operations.
Possible Effect
Disposal Alternatives
Area
Adjacent
to Channel
Trough
South of
Bay Bridge
Intensity of Effect
Increased Turbidity
of Water Column(D)
Temporary &
Local
Temporary &
Local
Increased Contaminant
Releases to Water
Column(E)
1. Metals
2. Nutrients
3. CHCs
Negligible
Negligible
Possible
Negligible
Negligible
Possible
Oxygen Depletion of
Water Column
Temporary &
Local
Temporary &
Local
See Appendices at end of report for documentation.
64
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Table 4 (Continued)
b. Ecological Effects during
disposal operations.
Disposal Alternatives
Area
Adjacent
to Channel
Trough
South of
Bay Bridge
Possible Effect
Intensity of Effect
(G)
Increased Turbidity
1. Phytoplankton
(Suppression of
Photosynthesis)
2. Zooplankton
3. Nekton (clogging
gills, etc.)
4. Benthos (clogging
gills, etc.)
(H)
Smothering of Benthos '
Exclusion and/or Attrac-
tion of Fish
(I)
Uptake of Contaminants
1. Metals
(a) Benthos
(b) Plankton
(c) Nekton
2. CHCs
(a) Benthos
(b) Plankton
(c) Nekton
(J)
Temporary &
Local;
Negligible
Negligible
Negligible
Negligible
Temporary &
Local;
Negligible
Negligible
Negligible
Negligible
May be complete;
temporary
May be complete;
temporary; fewer
organisms
Either; temporary Either; tempo-
Si local
Negligible
Negligible
Negligible
Possible
Possible
Possible
rary & local
Negligible
Negligible
Negligible
Possible
Possible
Possible
See Appendices at end of report for documentation.
65
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Table 4 (Continued)
c. Environmental effects
subsequent to disposal,
Disposal Alternatives
Possible Effect
Area
Adjacent
to Channel
Trough
South of
Bay Bridge
Intensity of Effect
Increased Turbidity in
lrr\
Water Columnv '
Contaminant Release
to Water(L)
1. Metals
2. Nutrients
3. CHCs
Oxygen Depletion of
Water Column(M)
Movement of Dredged Mate-
rial After Disposal
Effect of Changes in
Bottom Topography
1. Circulation
2. Uses (fishing &
boating)
Negligible
Unlikely
Small
Possible
Undetectable
Likely
Negligible
Small
Negligible
More unlikely
Small
Possible
Undetectable
Less Likely
Negligible
None
See Appendices at end of report for documentation.
66
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Table 4 (continued)
d. Ecological effects
subsequent to
disposal.
Disposal Alternatives
Area
Adjacent
to Channel
Trough
South of
Bay Bridge
Possible
Intensity of Effect
Time for recovery of
(P)
benthosv '
1. Biomass
2. Diversity
Increased metal uptake by
organisms
1. Metals
(a) Benthos
(b) Plankton
(c) Nekton
2. CHCs
(a) Benthos
(b) Plankton
(c) Nekton
<1.5 yr
<1.5 yr
Possible
Unlikely
Unlikely
Possible
Possible
Possible
<1.0 yr
<1.0 yr
Possible
Unlikely
Unlikely
Possible
Possible
Possible
See Appendices at end of report for documentation.
67
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CASE STUDY 2
THE ANALYSIS
Our second case study was for the Baltimore Harbor
Approach Channels, Fig. 21. We considered five disposal
options: (1) dredging and overboard disposal in areas adja-
cent to channels by hydraulic dredging and pipeline disposal,
or by bucket dredging and scow disposal, (2) hydraulic
dredging and pipeline disposal in confined, submerged areas
adjacent to channels, (3) bucket dredging and hopper barge
disposal at the Kent Island Dump Site, (4) bucket dredging
and hopper barge disposal in the trough south of the Bay
Bridge at Annapolis, and (5) hydraulic dredging and pipeline
disposal to create wetlands in fringing areas.
ncipal Findings, Conclusions., an
I. Most of the sediment accumulating in the
Baltimore Harbor Approach Channels comes from erosion
of the drainage basin of the Susquehanna River and
from erosion of the shoreline of Chesapeake Bay.
2. The sediments in the Baltimore Harbor
Approach Channels are not measurably different in
their physical and chemical characteristics and con-
taminant levels from sediments presently at the Kent
Island dump site or in areas adjacent to the channels
The data available (Table 6a) suggest that the con-
taminant levels of sediment in the Baltimore Harbor
Approach Channels may be elevated above contaminant
levels found in sediments of the trough south of
the Bay Bridge. However, because of differences in
analytical techniques used to evaluate the contami-
nant levels in these areas, the differences may not
be significant. Further analysis of sediment from
both areas (Baltimore Approach Channels and the
trough) should be performed by a single laboratory,
68
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especially for metals and CHCs. Analysis for
contaminants must be performed also at potential
fringing area disposal locations.
3. This portion of Chesapeake Bay is normally
subject to large fluctuations in ambient turbidity,
dissolved oxygen, temperature and salinity. Proc-
esses controlling these normal background conditions
must be considered in planning, executing, and
regulating dredging and disposal operations.
4. Naturally-deposited sediments and dredged
materials are resuspended and dispersed in this
region of Chesapeake Bay by tidal currents, turbu-
lence due to wind waves and ships' wakes, and the
long-term estuarine circulation. These processes
are most effective in shallow waters and least
effective in the deep trough of the central Bay.
Enclosing proposed disposal areas within structures
that nearly reached to the water surface would
significantly reduce sediment resuspension and the
dispersion of sediment from the disposal site.
5. It is unlikely that sediment-associated
metals in dredged materials from the Baltimore
Harbor Approach Channels will be made more avail-
able to benthic or water column biota during or
subsequent to disposal operations.
6. Sediment-associated organic compounds,
such as chlorinated hydrocarbons, deserve parti-
cular attention because of high toxicity at low
concentrations, significant potential for release
from sediment, public concern, and the scarcity of
data. We recommend that additional analyses of
sediment from all proposed disposal options be
made, and that the distribution coefficient of
CHC compounds between sediment and water be
routinely determined for each dredging project.
7. With the possible exception of the
69
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release of chlorinated hydrocarbon compounds, the
physical and chemical effects of the discharge
plume from dredging and disposal operations are
normally small and have no long-term effects on
organisms or environmental quality. We believe
the large effort currently spent to monitor DO,
turbidity, and metals during disposal operations
might better be expended in monitoring possible
releases of chlorinated hydrocarbons.
8. Depletion of dissolved oxygen by dredg-
ing and disposal is a local, transitory phenomenon
in shallow waters, and is unlikely to have a
measurable effect on dissolved oxygen levels in
near-bottom waters in the trough south of the
Bay Bridge.
9. Benthic communities in subaqueous
dredged material disposal sites recover to near-
normal abundances within one to two years.
Community diversity may take somewhat longer to
recover to pre-disposal levels. Recovery of
benthic abundance and diversity is expected to
be quicker in the deep trough in the central
Bay than in shallow waters of the upper Bay.
10. Containment of dredged materials or
utilization of disposal sites far from the
channels can be expected to decrease the fre-
quency of dredging required to maintain the
Baltimore Harbor Approach Channels. Submerged
containment will also significantly reduce the
potential for release of sediment-associated
contaminants to the water column subsequent to
disposal.
11. The deep trough in the central Bay
appears to be an attractive site for disposal
of uncontaminated sediments. There are, however,
several auestions that should be answered before
70
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the trough is considered as a disposal site.
a. To what extent is the trough used by
over-wintering fish? At what levels
in the water column do they congregate
and in what concentrations?
b. To what extent is the trough used by
blue crabs as an over-wintering area?
What parts of the trough do they utilize?
c. To what extent would disposal in the
trough alter its characteristic proper-
ties?
12. Because of the possibility of oxidizing dredged
materials and reducing the strength of the sediment-
contaminant association, creation of new wetlands has
significant potential for release of metals and other
contaminants to nearby waters and to organisms.
II
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CASE STUDY 2. BALTIMORE HARBOR APPROACH CHANNELS
Our second case study was for material dredged from
the Baltimore Harbor Approach Channels.
The Baltimore Harbor Approach Channels are shown in
Fig. 21. The rationale for the steps we followed in assess-
ing dredging/disposal options for this project are given in
Schubel et al. (1979). The steps are shown schematically
in Fig. 2.
Step ~. 'date? Quality Certificate
Since the Baltimore Harbor Approach Channels are collec-
tively an authorized U.S. Army Corps project, dredging of
them requires only a Water Quality Certificate. Under sec-
tion 10 of the Rivers and Harbors Act of 1899 (33 U.S.C.
S401 et. seq.) the U.S. Army Corps of Engineers is charged
with the responsibility of evaluating requests to make physi-
cal alterations in the navigable waters of the United States.
A dredging operation is such a physical alteration. The
District Office serves as a clearing house for other Federal,
State, and local agencies concerning the environmental
effects of a proposed action. The primary Federal agencies
reviewing applications for physical alterations to areas
under the aegis of the Baltimore District are the U.S.
Environmental Protection Agency, the U.S. Fish and Wildlife
Service of the Department of the Interior, and the National
Marine Fisheries Service of the Department of Commerce.
The decision to issue a Water Quality Certificate is
based on an evaluation of the probable impact of the proposed
activity on the public interest. That decision should reflect
the national concern for both protection and utilization of
important resources. The benefit which reasonably may be
expected to accrue from the proposal must be balanced
against its reasonably forseeable detriments. All factors
which may be relevant to the proposal are to be considered;
72
-------
Fig. 21 Map showing the approach channels
to Baltimore Harbor.
73
-------
among those are conservation, economics, aesthetics, general
environmental concerns, historic values, flood damage pre-
vention, land use classification, navigation, recreation,
water supply, water quality, and in general, the needs and
welfare of the people. No permit will be granted unless its
issuance is found to be in the public interest.
Step II. Characterization of Material to be Dredged
The State of Maryland requires that certain tests be
made to characterize materials proposed for dredging and
to characterize materials in the proposed disposal area.
These tests are listed in Table 5 which also indicates
which of the tests have been conducted for sediments in the
Baltimore Harbor Approach Channels and in selected disposal
areas. Characteristics of the materials accumulating in
the Baltimore Harbor Approach Channels and in selected
disposal areas are summarized in Table 6.
Step III. Identification of Potential
Dredging/Disposal Options
We evaluated five dredging/disposal options:
(1) hydraulic dredging and pipeline disposal, or
bucket dredging and slow disposal, overboard in areas
adjacent to the Channels,
(2) hydraulic dredging and pipeline disposal in con-
fined, submerged areas adjacent to Channels
(3) bucket dredging and hopper barge disposal at the
Kent Island Dump Site
(4) bucket dredging and hopper barge disposal in the
trough south of the Bay Bridge at Annapolis
(5) hydraulic dredging and pipeline disposal in
fringing areas to create wetlands.
The availability of data for comparative tests of
sediments in the five potential disposal sites is summarized
74
-------
in Table 4; the data themselves are summarized in Table 6.
Important characteristic properties of each of the five
disposal options are summarized in Table 7. The data
recorded are typical values.
Step IV. Assessment of Potential
Dredging/Disposal Options
The short-term and long-term environmental and ecologi-
cal effects of each of the dredging/disposal options we
evaluated are summarized in Table 8. We did not attempt to
evaluate the socio-economic factors (Step IVc, Fig. 2).
With respect to environmental and ecological effects
during disposal, there is little to choose among at least
four of the five disposal alternatives. The exception may
be wetland creation. Water column effects during disposal
are local, temporary and small for all five options. In
all five cases, disposal would result in the immediate
burial of most of the benthic organisms. The only potential
ecological effect during disposal we identified which we
could not assess with existing data was the uptake of
chlorinated hydrycarbons (CKCs) by plankton, benthos, and
nekton.
The potential environmental and ecological effects
subsequent to disposal are of greater concern because of
their greater uncertainty. The principal problems with
contaminants are not with metals as is commonly supposed.
All available evidence indicates that metals in dredged
materials do not pose a significant threat to the environ-
ment, to the biota, or to human health if the materials are
kept in a geochemical environment similar to that from
which they were dredged. According to Turekian (1974) "The
best-informed conclusion must be that, as far as metals are
concerned, what has been deposited with the dredge spoil
has little chance of leaching out of the sediment. The
problems of polluted dredge spoil dumping are thus more
75
-------
concerned with mobilized toxic organic compounds and changes
in the physical character of the substrate than xvith the
potentially toxic heavy metals."
Since metals and other contaminants may be taken up by
benthic organisms, particularly by those that burrow into
the sediment, appropriate choice of disposal areas can
minimize any potential problems. A disposal area should be
selected which minimizes the number of benthic animals that
are harvested directly from the disposal area, and which
minimizes the number of benthic organisms that serve as
food for animals that are harvested from that area or from
other areas of the Bay. The deep trough south of the Bay
Bridge has fewer benthic organisms per unit area than any
of the alternative disposal areas we evaluated. The benthic
population is essentially eliminated every summer because of
the nearly anoxic conditions that recur annually.
,We considered five dredging/disposal options for main-
tenance material dredged from the Approach Channels to
Baltimore Harbor: (1) dredging and disposal overboard in
areas adjacent to the Channels, (2) hydraulic dredging and
pipeline disposal in confined, submerged areas adjacent to
Channels, (3) bucket dredging and hopper barge disposal at
the Kent Island Dump Site, (4) bucket dredging and hopper
barge disposal in the trough south of the Bay Bridge at
Annapolis, and (5) hydraulic dredging and pipeline disposal
in fringing areas to create wetlands.
Based on our evaluation of existing data on environ-
mental and ecological effects subsequent to disposal, we
rank the five disposal alternatives in the following order
of decreasing acceptability (1) deep trough south of Bay
Bridge, (2) submerged, confined overboard adjacent to
channels, (3) Kent Island Dump Site, (4) overboard adjacent
to channels, (5) wetland creation.
-------
On environmental and ecological grounds, there is
little basis for selecting between the first two choices
and perhaps among the first four. Disposal in a confined,
submerged area has the disadvantages that a structure would
be needed to retain the material and it could interfere
with other uses of the area and pose a hazard to navigation.
Disposal at the Kent Island Dump Site is somewhat less
deisrable than the first two choices because of the some-
what greater chance of movement of the material and the
potential for uptake of contaminants by important benthic
organisms—oysters and clams.
Disposal overboard in areas adjacent to the Channels
increases the probability—relative to the first three
choices—of dispersal and of release of some contaminants
to the overlying water. Its principal disadvantage, however,
is that much of the material would return to the channels
and, hence, the frequency of dredging would be greater than
for any of the first three options. No persistent undesir-
able environmental or ecological effects have been documented
from overboarding material dredged from these channels.
We consider that use of materials dredged from the
Baltimore Harbor Approach Channels for wetland creation is
the least desirable of the alternatives we examined because
of the substantially increased probability of mobilization
of contaminants. This conclusion would be altered only if
a convincing case could be made for the need for wetland
habitat.
The deep trough appears to be an attractive site for
disposal of uncontaminated dredged materials. There are,
however, a number of questions that should be answered
before any disposal occurs. These were stated in Case Study
1 and are repeated here for emphasis.
(1) What is the distribution of over-wintering blue
crabs in the trough in space and in time?
(2) Would disposal of dredged materials substantially
increase the mortality of these crabs?
77
-------
(3) What is the distribution of over-wintering finfish
in the trough in space and in time?
(4) Would disposal of dredged materials from scows
disturb these populations of over-wintering fish?
If the deep trough south of the Bay Bridge at Annapolis
were to be designated as a disposal area for material
dredged from the Chesapeake and Delaware Canal Approach
Channel, the approved period for dredging and disposal, the
"dredging window," for these channels might have to be
adjusted.
78
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Table 6, Sources of Information
1. Metals, CHCs, volatile solids, oils and greases,
and water content data for Baltimore Harbor Approach
Channels and adjacent areas.
Cronin, W.B., M.G. Gross, W.R. Taylor, R.C. Whaley,
W. Boicourt, and J.R. Schubel. 1976. Investi-
gations of dredging operations, Brewerton Channel
Cut-off Angle—Patapsco River mouth disposal site,
10 April 1976 - 26 May 1976. Chesapeake Bay
Institute, The Johns Hopkins University, Open
File Rept. 10, 50pp. + appendices.
2. Metals data for Kent Island Dump site.
Villa, 0. and P.G. Johnson. 1974. Distribution
of metals in Baltimore Harbor sediments. Environ-
mental Protection Agency Tech. Rept. 59,
Annapolis, Md., Field Office, Region III, NTIS
EPA-903/9-74-012.
3. Clay mineral data.
Hathaway, J.C. 1972. Regional clay mineral facies
in estuaries and continental margin of the United
States East Coast. Pages 293-317 ir. B.W. Nelson
(ed.), Environmental Framework of Coastal Plain
Estuaries. Geological Society of America Mem.
133.
4. Sediment grain size data.
Ryan, J.D. 1953. The sediments of Chesapeake Bay.
Maryland Department of Geology, Mines, and Water
Resources, Bull. 12, 120pp.
5. Data for trough.
See sources enumerated for Table 2.
82
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CASE STUDY 3. THE ANALYSIS
Our third case study was for the Baltimore Harbor
channels, Fig. 22. We evaluated five disposal options:
(1) dredging and overboard disposal in areas adjacent to
the channels by one of the following combinations: hydraulic
dredging and pipeline disposal, or bucket dredging and pipe-
line disposal, or bucket dredging and scow disposal,
(2) Hydraulic dredging and pipeline disposal in confined,
submerged areas adjacent to channels, (3) a combination of
hydraulic dredging with pipeline and scow disposal techniques
to create an island, either inside or outside the harbor,
(4) a combination of hydraulic dredging and scow or pipeline
disposal in nearshore fringing areas to create or extend
wetlands, and (5) a combination of hydraulic or bucket
dredging and disposal at an unspecified upland site.
Principal Findings3 Conolusions, and Recommendations.
1. Most of the sediment accumulating in the
Baltimore Harbor Channels comes from erosion of the
drainage basin of the Susquehanna River and from
erosion of the shoreline of Chesapeake Bay.
2. The sediments in the Baltimore Harbor
Channels are highly contaminated with metals, PCBs,
and oils and greases. Close examination of the
extensive data available for metals (Table 10 and
Refs.) and more limited data for CHCs suggest that
Inner Harbor sediments (Fort McHenry Channel) are
significantly more contaminated than Outer Harbor
(Brewerton Channel) materials.
3. With the exception of CHCs, which may be
solubilized during disposal operations, the poten-
tial disposal options for Baltimore Harbor materials
are not limited by the possible release of contami-
nants during disposal operations. Because our ability
88
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to predict the possible remobilization of contami-
nants in the period subsequent to disposal is
limited by lack of information, great care should
be exercised in the choice of disposal option.
4. Oxidation of reduced dredged materials
significantly enhances the possibility of solubili-
zation of metals to the water column.
5. Resuspension and dispersal of dredged
sediment, by increasing surface area available for
exchange with water, significantly increases the
rate of dissolution of contaminants, including CHCs.
6. Although the characteristics of artificial
islands required to physically contain the dredged
sediment probably have been adequately addressed,
much more study is needed of the possible geochemi-
cal consequences of subaerially exposing previously
reduced sediment in artificial islands. Such studies
must account for the motion and oxidizing ability of
rainwater and runoff, on the surface of the island
and groundwater in its interior. Present geo-
chemical theory of sediment suggests that these
waters have significant potential to act as vectors
of dissolved contaminants to nearby waters.
7. Confining highly contaminated dredged
materials underwater minimizes oxidation and
resuspension, limiting the potential release of
contaminants.
8. Confinement of highly contaminated materials
underwater at the base of an island may be acceptable
if studies can demonstrate convincingly that develop-
ment of a local oxygenated water table will not occur
and that there will be no motion of groundwaters
through the structure.
9. Upland disposal, because of the high
probability of oxidation of the dredged sediment,
is highly likely to result in mobilization of
contaminants by runoff and groundwater.
89
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CASE STUDY 3. BALTIMORE HARBOR CHANNELS
The third and final case study we made was for material
dredged from Baltimore Harbor Channels. Baltimore Harbor
Channels are shown in Fig. 22. The rationale for the steps
we followed in assessing the dredging/disposal options are
described in Schubel et al. (1979) and shown schematically
in Fig. 2.
Water Quality Cevtifiaate Application
Since the Baltimore Harbor Channels are collectively an
authorized U.S. Army Corps project, dredging requires only a
Water Quality Certificate. Under Section 10 of the Rivers
and Harbors Act of 1899 (33 U.S.C. S401 et. seq.) the U.S.
Army Corps of Engineers is charged with the responsibility
of evaluating requests to make physical alterations in the
navigable waters of the United States. A dredging operation
is such a physical alteration. The District Office serves
as a clearing house for other Federal, State, and local
agencies concerning the environmental effects of a proposed
action. The primary Federal agencies reviewing applications
for physical alterations to areas under the aegis of the
Baltimore District are the U.S. Environmental Protection
Agency, the U.S. Fish and Wildlife Service of the Department
of the Interior, and the National Marine Fisheries Service
of the Department of Commerce.
The decision whether to issue a Water Quality Certificate
is based on an evaluation of the probable impact of the pro-
posed activity on the public interest. That decision should
reflect the national concern for both protection and utiliza-
tion of important resources. The benefit which reasonably
may be expected to accrue from the proposal must be balanced
against its reasonably forseeable detriments. All factors
which may be relevant to the proposal are to be considered;
araong those are conservation, economics, aesthetics, general
90
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2
3
4
1O
WEST CHANNEL
EAST CHANNEL
SPRING GARDEN CHANNEL
PERRY 3AR CHANNEL
FT McHENRY ANCHORAGE
FT McHENRY CHANNEL
CURTIS BAY CHANNEL
MARINE CHANNEL
SPARROWS PT CHANNEL
BPEWE3TON CHANNEL
CUTOFF ANGLE
-v^
H^=
^
^_
-, * /^
^<-'^
^
^^/fty-
•"••W
(
- N
-\
^^J ^/
Jr^ -^^
£ V
Fic. 22
Map showing Baltimore Harbor Channels.
91
-------
environmental concerns, historic values, flood damage preven-
tion, land use classification, navigation, recreation, water
supply, water quality, and in general, the needs and welfare
of the people. No permit will be granted unless its issu-
ance is found to be in the public interest.
Step II. Cha?aste?ization of Material
to "o e
The State of Maryland requires that certain tests be
made to characterize materials proposed for dredging and to
characterize materials in the proposed disposal area. These
tests are listed in Table 9 which also indicates which of
the tests have been conducted for sediments in Baltimore
Harbor Channels and in the disposal areas we selected for
analyses. Characteristics of the materials accumulating in
Baltimore Harbor Channels and in the disposal areas we con-
sidered are summarized in Table 10.
Identification of Potential
Dredging/Disposal Options
We evaluated five dredging/disposal options:
(1) hydraulic dredging and pipeline disposal or bucket
dredging and scow disposal, overboard in areas adjacent to
the channels,
(2) hydraulic dredging and pipeline disposal in con-
fined, submerged areas adjacent to channels,
(3) a combination of hydraulic dredging with pipeline
and scow disposal techniques to create an island, either
inside or outside the harbor,
(4) a combination of hydraulic dredging and scow or
pipeline disposal in nearshore fringing areas to create or
extend wetlands,
(5) a combination of hydraulic or bucket dredging and
disposal at an unspecified upland site.
92
-------
The availability of data for comparative tests of sedi-
ments in potential disposal sites is summarized in Table 9;
the data themselves are summarized in Table 10. Important
characteristic properties of the potential disposal sites
are summarized in Table 11. The data recorded are typical
values.
Step IV. Assessment of Potential
Dredging/Disposal Options
We assessed the probably short-term and long-term
environmental and ecological effects of each of the five
dredging/disposal options using existing data, Table 12. We
did not attempt to evaluate the socio-economic factors (Step
IVc, Fig. 2).
With respect to environmental and ecological effects
during dredging and disposal, there is little to choose among
at least three of the five alternatives. Wetland creation
and island construction may be exceptions, but even for these
any adverse effects during dredging and disposal are expected
to be transitory and small. All available data indicate that
water column effects during dredging and disposal are local
in extent, temporary, and small. In every disposal alterna-
tive we examined, except upland, disposal would result in
the immediate burial of most of the benthic organisms. The
only potential effect during dreding and disposal which we
identified which we could not assess with existing data was
the uptake of chlorinated hydrocarbons (CHCs) by plankton,
benthos, and nekton.
The potential environmental and ecological effects
subsequent to disposal are of greater concern because of
their greater uncertainty and their greater potential for
adverse impact. It is ironic that we have less information
to predict the environmental and ecological effects of dis-
posal of materials dredged from Baltimore Harbor than we do
for materials dredged from Baltimore Harbor Approach Channels
93
-------
and particularly for those materials dredged from the
Chesapeake and Delaware Approach Channel. This is a matter
of concern since much of the material dredged from Baltimore
Harbor is contaminated while materials dredged from the other
two projects are not. The potential for adverse environmental
and ecological effects are far greater for materials dredged
from Baltimore Harbor than for materials dredged from either
of the other projects we considered.
Metals in dredged sediment are not the principal environ-
mental problems as is commonly supposed. All available
evidence indicates that metals in dredged materials do not
pose a significant threat to the environment, to the biota,
or to human health if the materials are kept in a geochemical
environment similar to that from which they were dredged.
According to Turekian (1974) "The best-informed conclusion
must be that, as far as metals are concerned, what has been
deposited with the dredge spoil has little chance of leaching
out of the sediment. The problems of polluted dredge spoil
dumping are thus more concerned with mobilized toxic organic
compounds and changes in the physical character of the sub-
strate than with the potentially toxic heavy metals."
Since metals and other contaminants may be taken up by
benthic animals, particularly by those that burrow into the
sediment, appropriate choice of disposal areas can minimize
any potential problems. A disposal area should be selected
which minimizes the number of benthic animals that are
harvested directly from the disposal area, and which mini-
mizes the number of benthic animals that serve as food for
animals that are harvested from that area or from other areas
of the Bay.
Conclusions and P.ecommenda.t'icns
We considered five dredging/disposal options for main-
tenance material dredged from Baltimore Harbor Channels:
(1) dredging and overboard disposal in areas adjacent to the
94
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channels, (2) hydraulic dredging and pipeline disposal in
confined, submerged areas adjacent to channels, (3) a combina-
tion of hydraulic dredging with pipeline and scow disposal
techniques to create an island either inside or outside the
Harbor, (4) a combination of hydraulic dredging with pipeline
or scow disposal in nearshore finging areas to create or
extend wetlands, and (5) a combination of hydraulic or bucket
dredging and disposal at unspecified upland disposal sites.
Based on our evaluation of existing data on environ-
mental effects we rank the five disposal alternatives in the
following order of decreasing acceptability: (1) hydraulic
dredging and pipeline disposal in confined submerged locations
adjacent to Harbor channels, (2) overboard disposal adjacent
to Harbor channels in unconfined locations, (3) marsh crea-
tion, (4) island construction, (5) upland disposal. On
environmental and ecological grounds the first two alterna-
tives are more acceptable than the latter three. Disposal
of Harbor sediments at submerged locations within the harbor
is much less likely to cause the release of associated con-
taminants than the latter three alternatives, each of which
involves subaerial exposure of the dredged sediment. Dis-
posal within a confined, submerged structure is preferable
to unconfined overboard disposal because confinement will
minimize disturbance of the dredged material, decrease the
likelihood of mobilization of contaminants, and limit the
return of the dredged material to the channels. This will
reduce the frequency of maintenance dredging required.
We consider those options—island construction, marsh
creation, and upland disposal—that result in subaerial
exposure of the dredged material less desirable than sub-
merged disposal because of the higher probability of release
of the sediment-associated contaminants to surrounding water
or groundwater. If the exposed part of the island were
constructed entirely of uncontaminated sediments, and if the
island were surrounded by an impermeable dike, many of our
objections would be removed.
95
-------
For contaminated materials dredged from the Harbor, dis-
posal options should be selected which minimize the movement
of the particles; the mobilization of the contaminants from
the particles; and the uptake of contaminants by organisms,
including people. Construction of containment/island disposal
facilities is one approach to the problem. Another method is
burial beneath the Bay floor and capping with clean material.
Construction of a large disposal island/containment
facility is an essentially irreversible decision. It
represents a permanent sacrifice of a segment of the Bay for
this purpose. Because of this, and also because of the
expense involved, construction of such a facility should be
undertaken only after careful analysis and thorough assess-
ment of the full range of alternatives. Environmentally and
ecologically, the most compelling argument for construction
of an island/containment facility is to isolate contaminants
from the environment and the biota, including people.
Environmental conditions should be selected which minimize
both movement of the contaminated particles themselves and
the release (mobilization) of the contaminants from the
particles and their movement in solution. This indicates
that to maximize containment of the contaminants, the con-
taminated particles should be confined by barriers and kept
submerged beneath the surface of the Bay at all stages of
the tide. If contaminated materials are deposited above the
water surface a number of potential problems must be care-
fully evaluated. These include: (1) contaminant movement in
groundwater, (2) release of contaminants by pumping action
resulting from alternate wetting and drying of the materials,
(3) uptake of contaminants by plants, and (4) release of
contaminants in runoff.
Since construction of an island/containment facility is
expensive and permanently sacrifices a segment of the Bay,
the underwater storage capacity of such a facility should be
reserved for contaminated materials.
There will be a continuing need to find a site suitable
96
-------
for disposal of contaminated materials dredged for mainte-
nance of Baltimore Harbor channels. A proper facility would,
in our opinion, be one designed and managed to accept only
contaminated materials until it had been filled nearly to the
water surface and one large enough to accomodate materials
generated over a relatively long period of time, at least
several decades. If such a facility were to be used for
construction of the proposed 50 foot channel, materials that
would be dredged should be assessed for their contaminant
levels. If, as we expect, the more deeply-buried materials
are uncontaminated, openwater disposal should be considered
for these materials, reserving the containment facility for
contaminated sediments. If it is desirable to extend the
dredged material above the water surface to create an island,
this should be done with uncontaminated materials.
97
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Table 9 Comparative tests required by State of Maryland's
Department of Natural Resources for materials
proposed for dredging and for materials in pro-
posed disposal areas. An X in the Table indicates
that data exist. Wetland and upland disposal
sites have not been included in the Table.
Parameter
Volatile Solids
Chemical Oxygen Demand
Hexane Extractables
Total Organic Carbon
Zinc
Mercury
Cadmium
Copper
Chromium
Lead
Total Keldjahl Nitrogen
Total Phosphorous
Chlorinated Hydrocarbons
Particle Size
Baltimore
Harbor
Channels
X
X
X
X
X
X
X
X
Overboard
Areas
Adjacent
to
Channels
X
X
X
X
x
X
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X
X
X
X
X
X
X
X
X
X
98
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Table #10 Sources of Information
1. Metals Data for Baltimore Harbor Channels and
Adjacent Areas from:
Villa, 0. and-P.G. Johnson. 1974. Distribution
of metals in Baltimore Harbor sediments. Tech.
Kept. #59, Annapolis, Md., Field Office, Region
III, Envir. Prot. Agency., NTIS SEPA-903/9-74-012
2. CHC and Oils and Greases Data from:
Tsai, C., J. Welch, K. Chang, J. Schaeffer,
L. Cronin. 1979. Bioassay of Baltimore Harbor
sediments. Estuaries 2:141-153.
100
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APPENDIX A
l-ecree of Turbulence at Proposed Disposal Sites for
Chesapeake and Delaware Canal Approaches Materials
rTable 3}.
Bottom water turbulence originates from three sources
of energy input: wind waves, tidal forces, and laden ships'
wake. Two of these, wind waves and ships' wake, have their
origin at the water surface. Tidal energy is transmitted
throughout the water column. Because wave energy becomes
less intense as depth increases, bottom waters in deeper
areas are subject to less wave induced turbulence than shal-
lower areas. It is quite rare that wind waves generated in
Chesapeake Bay have the ability to affect bottom waters in
the deep trough (average depth 30m), but wind waves must
frequently affect bottom waters in the shallow (average
depth 4 m) waters of the northern Bay.
An additional source of turbulent energy to the bottom
waters of the northern Bay is the wake resulting from the
passage of heavily laden ships. These waves, 1 to 2 m in
height, propagate longitudinally in the estuary from the
channel, and have the ability to significantly stir bottom
waters.
Tidal forces cause an oscillatory flow in both the
shallow waters of the overboard disposal areas of the northern
Bay and the bottom waters of the deep trough. During the
approximately six hours of the ebb half-tidal cycle, the flow
is directed down the Bay toward the ocean, while during the
flood, half-tidal cycle the flow is directed toward the head
of the Bay. Except in the upper Bay, during periods of high
river inflow, these tidal flows are large (on the order of
five to ten times the flows required to move the fresh water
seaward) and density driven two-layered estuarine flow results.
Winds, both local winds blowing on the surface waters of the
upper Bay and the mid-Bay, and remote winds blowing over the
106
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lower reaches of the Bay and even on the continental shelf
produce aperiodic currents in the upper and raid-Bay which
at times approach the speed of the pure tidal currents.
The magnitudes of the peak ebb and flood velocities in
the shallow overboard disposal areas of the upper Bay and
those in the near bottom waters of the deep trough are very
similar; about 40 to 50 cm per second. However, because the
frictional effects of the side boundaries of the narrow
trough are added to the effects of bottom friction, the
tidal velocities in the turbulent boundary layer within
about one meter of the bottom in the trough are less than
those in the same layer above the bottom in the shallow
overboard disposal area. Also, the wind induced currents
which sometimes add to the flood flow and sometimes add to
the ebb flow are stronger in the shallow waters of the
overboard disposal areas of the upper Bay than in the deep
waters of the trough. Note that this effect of the wind is
quite distinct from the turbulence induced by wind generated
waves. In any case, the tidal currents, and even more
particularly, the combined tidal and wind currents, result
in more resuspension of the bottom sediments in the shallow
overboard disposal areas of the upper Bay than in the deep
trough below the Bay Bridge.
The bottom waters of the northern Chesapeake Bay are
more turbulent than the bottom waters of the central Bay
because their shallow depth makes them susceptible to two
sources of turbulence, wind waves and ships wake, which do
not affect deeper bottom waters in the central Bay.
107
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APPENDIX B
Anoun~ of Sedinsnt Eesuspension at Proposed Disposal
5i~es for Materials Dredged from Chesapeake and
Delaware Canal Approach Channel (Table Z)
Bottom sediment resuspension is determined by the
degree of near-bottom turbulence and the shear strength of
the surficial sediments. The shear strength is determined
by a variety of factors, including grain size, state of
particle agglomeration, and water content. Agglomeration of
sediment grains is the result of activities of microorganisms
in the sediment that secrete mucoid films which bind sedi-
mentary particles (Rhoads, et al., 1978), of filter feeding
organisms on the bottom and in the water column, and of
physico-chemical processes (flocculation) that bind parti-
cles together. These agglomerates may be broken down by the
feeding activities of burrowing organisms, principally
protobranchs, tube worms, and other organisms living at or
near the sediment-water interface, which act to stabilize
the surface and enhance its resistance to erosion. Erodabil-
ity of sediment is thus a complicated function of particle
size and benthic community structure.
Although sediments in the deep trough and upper bay
disposal areas are similar in their basic textural proper-
ties—both are fine-grained—observational evidence (Schubel,
unpublished data) indicates a given tidal current speed, less
sediment is resuspended in the trough than in the upper bay.
This effect may be due to a difference in benthic community
structure at the two locations. Few data are available to
establish this however. Because the sedimentation rate in
the trough is an order of magnitude less than the rate in
the upper reaches of the Bay (Schubel and Carter, 1977)
surficial sediments in the trough have had an order of
magnitude more time available to become agglomerated and
stabilized than upper bay sediments--assuming the rates of
108
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binding are similar. Equally important, the energy available
from wind waves for sediment resuspension in the trough is
significantly less (see Appendix A) than in the upper Bay
because of the trough's much greater depth.
Although the processes that control the long term
stability of sediments at the two proposed disposal sites
remain obscure, observations show that in addition to being
more resistant to erosion, the sediments of the trough are
subject to less intense erosional forces. Bottom sediment
resuspension is a much more important geological process in
the northern Bay than in the trough.
Eefevenaes
Rhoads, D.C., P. McCall, J.Y. Yingst. 1978. Disturbance
and Production on the Estuarine Seafloor. American
Scientist 66:577-583.
Schubel, J.R. and H.Y. Carter. 1977. Suspended sediment
Budget for Chesapeake Bay, Vol. 2 -In M. Wiley, (ed.),
Estuarine Research: Recent Advances, Academic Press.
250 pp.
109
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APPENDIX C
Effsots of Disposal Options on ~he Frequency of Dredging
Esquired to '.-lainzain the Chesapeake and Delaware
Approach Channel. (Table 3).
An undetermined, but probably significant, fraction of
the dredged materials disposed overboard alongside the
channel in the upper Bay is returned to the Channel as a
result of resuspension and fluid mud flow. Disposal of the
dredged material completely outside of this area, or in
confined areas, would eliminate return of this sediment to
the channel and therefore decrease the frequency of dredging
required to maintain the Chesapeake and Delaware Approach
channel. The decreased cost of dredging would at least
partially offset the added costs of disposal.
110
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APPENDIX D
ent of Excess Turbidity Generated
isposal Operations . (Table 4a)
Schubel et al. (1978) have considered in detail the
extent of turbidity generated by open-water pipeline disposal
operations. Of the material discharged during disposal,
between 90% and 99% by mass settles directly to the bottom
as a density flow. Excess turbidity plumes therefore
contain only between 1 and 10% of all the material dredged
and discharged. The spatial extent of the dredged material
plume is determined by the mean grain size of the sediment,
the depth of the water, and the dispersal characteristics of
waters at the disposal site.
During a pipeline dredging operation in the upper
Chesapeake Bay in 1966, Biggs (1970) observed that the con-
centration of total suspended sediment in the turbidity
plume fell to less than 50 mg/£ within 3.5 km of the dis-
charge. Since this was total, not excess, suspended sediment,
the actual size of the plume produced by the discharge was
less than this. Theoretical calculations (Wilson, 1979)
substantiated by field measurements (Schubel et al., 1978)
using the mean grain size of sediments from upper Chesapeake
Bay, indicate that six hours after disposal operations cease,
maximum concentrations in the turbid plume would have dropped
to one-tenth their initial values. Twelve hours later these
values would be one-hundredth the levels at six hours. This
same theory can predict the spatial and temporal extent of
turbidity plumes generated by open water pipeline disposal
before a dredging project is undertaken, for a wide variety
of conditions. This is a valuable tool for managers; one
which can be used to predict the local influence of excess
turbidity in the disposal area. Field observations obtained
to verify this model in several estuaries showed that while
the spatial extent of turbidity varied with local conditions,
111
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2
it never exceeded 1 km and the area of highest turbidities
was usually less than 1/10 this area.
Gordon (1974) considered the turbidity effects and
dispersion of dredged materials dumped into nearshore waters
by scow and hopper dredge. He concluded that 99% of the mass
of material rapidly reaches the bottom as a density current.
Three stages in scow disposal of dredged materials have been
recognized (Bokuniewicz et al., 1978): descent, impact, and
surge. Dredged materials released into the receiving waters
fall either as a high density current of dispersed particles
or as large sediment aggregates or "clods" which fall at
nearly constant velocity and entrain large volumes of water.
The impact point of this sediment jet can be predicted with
good accuracy if the ambient current structure is known.
Because much of the initial potential energy of the dredged
material is used up in accelerating entrained water, the
density jet strikes the bottom with relatively little kinetic
energy and produces only a small impact. A radial bottom
surge is created by the impact of the dredged material in the
form of a density current. The greatest thickness of this
surge has been found to be about 15% of the water depth. The
radius of the surge is between 150 and 300 m from the point
of impact and deposition begins to occur about 100 m from the
impact area.
The characteristics of the disposal pile and the effect
upon the water column are mostly determined by the mechanical
properties of the dredged material, the speed at which the
material is discharged into the water, the water depth, and
the current in the receiving waters. The kind of dredge has
a major effect on the mechanical properties of the sediment
after dredging and disposal. Mechanical dredging alters the
-in-situ mechanical properties of material less than hydraulic
dredging. It is important that the less cohesive the dredged
materials are, the greater the surface/volume ratio of the
deposited pile will be. Strong currents do not result in a
dispersion of the dredged materials during disposal and they
112
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are not necessarily a cause of inaccurate placement in a
designated area.
After disposal, residual turbidity in the water column
amounts to less than 1% of the total amount of material dis-
charged. This material settles from suspension over a period
of several hours and may drift with tides and currents during
that time.
References
Biggs, R.B. 1970. Project A, Geology and hydrography.
Pages 7-15 in Gross Physical and Biological Effects of
Overboard Spoil Disposal in Upper Chesapeake Bay. Natural
Resources Inst., Special Kept. 13, Ches. Biol. Lab.,
Univ. of Md.
Bokuniewicz, J. Gebert, R.B. Gordon, J. Higgins, P. Kaminsky,
C. Pilbeam, M. Reed, G. Tuttle. 1978. Field study of the
mechanics of the placement of dredged material at open-water
disposal sites. V.I Main Text and Appendices A-l.
U.S.A.C.E. Dredged Material Research Program Tech. Rept.
D-78-7. 99pp with Appendices.
Gordon, R.B. 1974. Dispersion of dredge spoil dumped in
nearshore waters. Est. Coast. Mar. Sci. 2:349-358.
Schubel, J.R., H.H. Carter, R.E. Wilson, W.M. Wise, M.G. Beaton,
and M.G. Gross. 1978. Field investigations of the nature
degree and extent of turbidity generated by open-water
pipeline disposal operations. Tech. Rept. D-78-30, U.S.
Army Engineer Waterways Experiment Station, Vicksburg, Miss.
Wilson, R.E. 1979. A model for the estimation of the
concentrations and spatial extent of suspended sediment
plumes. Est. Coast. Mar. Sci. 9:65-79.
113
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APPENDIX E
Contaminant Releases to Water Column During disposal
of Material Dredged From Chesapeake and Delaware
Canal Approach Channel (Table 4c).
I. Metals
No significant release of metals has ever been observed
during aquatic disposal operations in the U.S. (Wright et al.,
1978). The chemical equilibria that govern the solubility of
metals in the presence of sediment do not appear to be
affected by the disposal process. This is partly because of
the rapidity of descent and consolidation of the dredged
materials which provide limited time for oxidation. It is
also because of the variety of chemical mechanisms that are
responsible for the strength of the sediment-metal binding
relationships.
Metals become bound to fine-grained sediments principally
by three mechanisms: (1) they become bound to sediment-
associated organic matter, (2) they precipitate as insoluble
sulfide compounds under reducing conditions, and (3) they
co-precipitate with those metals (Fe and Mn) that are
insoluble under oxidizing conditions. It appears that the
generally extremely low dissolved metals concentrations in
nearshore waters are the result of these effects (Turekian,
1977) .
Because the dredged materials under consideration here
contain metals concentrations that are not significantly
elevated over the metals levels in sediments naturally
accumulating in the proposed disposal areas, and because
geochemical theory can adequately explain the field results
which show essentially no metals released to solution during
disposal operations, such release should not be considered
an environmental hazard at the locations under consideration
in this reoort.
114
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According to Turekian (1974), "The best-informed con-
clusion must be that as far as metals are concerned, what
has been deposited with the dredge spoil has little chance
of leaching out of the sediment. The problems of polluted
dredge spoil dumping are thus more concerned with mobilized
toxic organic compounds and changes in the physical charac-
ter of the substrate than with the potentially toxic heavy
metals."
2. Nutrients
Only minor nutrient releases have been observed during
open water disposal operations (Wright et al., 1978). These
are associated with dilution of the dredged material pore
waters during disposal. The extent of nutrient increases,
where observable, was always confined to the spatial extent
of the turbidity plume. Flemer (1970) investigated the
release of nutrients from an open-water pipeline disposal
operation for material dredged from the C & D Approach
Channel between November 1965 and November 1968. He reported
that total phosphate and nitrogen levels were increased by
factors of 50 and 1,000 respectively, but that the increases
were local and did not persist.
Excess nutrient levels in the water column may have two
effects: to increase plankton biomass by stimulating primary
productivity, and to poison organisms by high nutrient levels,
especially of NH..
Biostimulation is probably prevented from occurring by
reduced light levels associated with increased turbidity
during disposal. Flemer's (1970) investigation in the upper
Bay did not show any detectable effects of increased nutrient
levels on primary productivity. Nutrients released during
disposal operations have never been observed to reach levels
toxic to water column organisms, plankton or nekton.
3. CHCs
The interaction of chlorinated hydrocarbons with abiotic
and biotic constituents of the marine ecosystem is enormously
complex and cannot be evaluated from fundamental physical and
115
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biochemical considerations at the present time. Experiments
designed to determine the relative rate of release of CHC
compounds from dredged sediment (Fulk et al., 1975) have
failed to detect significant correlation between such release
and standard environmental factors (temperature, salinity, pH,
dissolved 0-)- Because of this, most investigators have
adopted the use of an empirical distribution coefficient K,
where K is the ratio of the concentration of CHCs in two
phases; usually a biotic or sediment phase (numerator) and
in solution (denominator) (Pavlou and Dexter, 1979; Dexter
and Pavlou, 1978; Faust, 1978; Choi and Chen, 1976). Although
K has not been determined for Chesapeake Bay sediment, typi-
4
cal values for other estuaries approximate 10 . Persistent
release from sediment may occur if dissolved CHC concentra-
tions are less than this factor smaller than sediment values.
Since the average PCB concentration per gram of upper bay
bottom sediment is 0.9 x 10 and in water 0.1 x 10
(Munson, 1975), K is exceeded and release of CHCs to solution
during dredging and disposal operations may be possible.
These results suggest that caution must be exercised in
the disposal of dredged materials highly contaminated with
CHCs, but provide little information to evaluate strategies
designed to minimize CHC release during dredging and disposal.
The distribution coefficient between dissolved and solid
phases is probably low enough so that CHC release to water
will occur with relatively uncontaminated upper Bay sediment.
Because it is an equilibrium process, release may be minimized
by providing minimum dilution of sediment during dredging.
We make, therefore, two recommendations. First, that the K
value for water-sediment interaction in the Chesapeake Bay
be determined, preferably for each dredging project. We also
recommend that the feasibility of clamshell dredging be
studied in both the upper bay and other dredged areas, since
this type of dredging minimizes the dilution of dredged
sediment.
116
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References
Choi, W.W. and K.Y. Chen. 1976. Associations of Chlorinated
Hydrocarbons with Fine Particles and Humic Substances in
Nearshore Surficial Sediments. Envir. Sci. Tech. 10:782-786
Dexter, R.N. and S.P. Pavlou. 1978. Distribution of stable
organic molecules in the marine environment: physical
chemical aspects. Chlorinated Hydrocarbons. Mar. Chem.
7:67-84.
Flemer, D.A. 1970. Project B, Phytoplankton. Pages 16-25
in Gross Physical and Biological Effects of Overboard Spoil
Disposal in Upper Chesapeake Bay. Natural Resources Inst.,
Special Kept. £3, Ches. Biol. Lab., Univ. of Md.
Fulk, R., D. Gruber and R. Wallschleger. 1975. Laboratory
study of the release of pesticide and PCB materials to the
water column during dredging and disposal operations.
Contract Report D-75-6, U.S. Army Engineer Waterways
Experiment Station, Vicksburg, Miss.
Pavlou, S.P. and R.N. Dexter. 1979. Distribution of PCB in
Estuarine Ecosystems. Testing the concept of equilibrium
partitioning in the Marine Environment. Envir. Sci. Tech.
13:65-76.
Turekian, K.K. 1977. The fate of metals in the oceans.
Geochem. Cosmochem. Acta. 41:1139-1144.
Turekian, K.K. 1974. Heavy metals in estuarine systems.
Oceanus 18:32-33.
Wright, T.D., D.B. Mathis, J. Brannon. 1978. Aquatic Dis-
posal Field Investigations: Galveston, Texas Offshore
Disposal Site, U.S.A.C.E. Dredged Material Research
Program Tech. Rept. D-77-20. 89pp.
117
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APPENDIX F
ft ate? Column During Disposal
of Material- Dredged from ~-'ne C'nesapea'K.3 and De laware
Canal Approach d~na.r.ne Is (Table 4 a.) .
Oxygen depletion of the water column during dredged
material disposal operations is caused by the chemical oxida-
tion of reduced compounds such as FeS which are normally
abundant in fine-grained estuarine sediments. Bacterial
action is too slow to measureably affect the water column
during disposal operations (Gross et al., 1976). Numerous
field investigations of the disposal of dredged materials at
various localities including: Columbia River (Boone et al.,
1978); Galveston Bay (Wright et al., 1978); Atchafalaya
estuary, Corpus Christi Bay and Appalachacola Bay (Schubel
et al., 1978); and upper Chesapeake Bay (Gross et al., 1976;
Cronin and Gross, 1976) have established that depletion of
dissolved oxygen during dredging/disposal operations is
confined approximately to the spatial and temporal extents
of the associated turbidity plume (see Appendix N).
Gross et al. (1976) compared the calculated oxygen
demand resulting from dredged material disposal in upper
Chesapeake Bay with the quantity of oxygen available in the
water affected by the disposal operation. Their results
showed that for dredged material with an initial oxygen
demand of 300 g/m of sediment and a final demand of 75 g/m
of sediment (measured values for upper bay sediments, see
Table #2) there was, under "worst case" conditions, enough
oxygen in a disposal area of 2.56 km (1 mi ) with an average
depth of 3.5 m (10 ft) to satisfy 48 days of continuous
discharge of dredged materials at a rate of 1000 in /hr.
Worst case conditions were defined to be typical, low summer
dissolved oxygen levels and no importation of dissolved
oxygen into the disposal area either from the atmosphere or
from contiguous segments of the Bay.
118
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If more reasonable conditions are considered, including
tidal mixing, the oxygen supply of the disposal area is more
han 8,000 times the total oxygen demand associated with the
dredged materials. If the water column is well mixed, the
oxygen sag associated with the discharge would be virtually
undetectable. Conditions in the middle Bay are even more
favorable because of the greater depth which provides more
opportunity for dilution during discharge. Also, the deepest
water in the trough south of the Annapolis Bay Bridge becomes
naturally anoxic in the summer time. Disposal of dredged
sediment into this area at this time would probably have no
effect upon the oxygen levels near the bottom. The effect
on upper water layers remains unevaluated.
The spatial scale of oxygen depletion during disposal
2
operations is of the order of km and the temporal scale is
limited to hours after disposal stops. Because of the semi-
diurnal nature of the tidal currents in Chesapeake Bay, the
turbidity plume and the associated plume of oxygen depression
shift location every six hours with a new plume forming on
each ebb and flood tide. The area affected by the old plume
recovers approximately to background pre-disposal, oxygen
levels within hours after tide turns.
The extent of water column oxygen depletion is partially
determined also by the type of disposal operation used.
Pipeline disposal, which tends to create a more dilute,
slowly settling, turbidity jet than hopper disposal, will
probably have a somewhat greater effect on water column
oxygen concentrations. This is because the greater sediment
transit time from the water surface to the bottom allows more
sediment oxidation which utilized dissolved oxygen. Also,
the greater surface area of the resultant pipeline deposit
will create a greater oxygen demand on the overlying waters.
119
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,-e ~e^enass
Boone, C.G., M.A. Granat, !!.?. Farrell. 1978. Aquatic dis-
posal field investigations; Columbia River Disposal Site,
Oregon. Tech. Rept. D-77-30 U.S.A.C.E., Dredged Material
Research Program.
Cronin, W. and M.G. Gross (1976). Environmental effects of
hydraulic dredging operations in Northern Chesapeake Bay.
Approaches to Chesapeake and Delaware Canal (Pearce Creek
Onshore Disposal) 14 Feb.-17 March 1976. Final Report to
State of Md. Dept. Natural Res. Open File Report #7,
Chesapeake Bay Inst., Johns Hopkins University, 25pp with
Appendices.
Gross, M.G., W. Taylor, R. Whaley, E. Hartwig and W. Cronin.
1976. Environmental effects of dredging and dredged
material disposal, Approaches to Chesapeake and Delaware
Canal, Northern Chesapeake Bay. Open File Report #6,
Chesapeake Bay Inst., Johns Hopkins University. 87pp plus
Appendices.
Schubel, J.R., H.H. Carter, R.E. Wilson, W.M. Wise,
M.G. Heaton, and M.G. Gross. 1978. Field investigations
of the nature, degree, and extent of turbidity generated
by open-water pipeline disposal operations. Tech. Rept.
D-78-30, U.S.A.C.E. Dredged Material Research Program.
120
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APPENDIX G
Ecological effects of inc~?ec,sed water co
turbidity during disposal of Chesapeake and
Delaware Canal Approaches Material (lable 41:),
1. Phytopiankton
Reductions in incident illumination and the consequent
possible decrease in phytoplankton photosynthetic activity
as the result of increased water column turbidity are con-
fined to the temporal and spatial limits of the turbidity
plume. Because this plume is transitory and local (see
Appendix D) in extent, associated decreases in phytoplankton
photosynthesis are also temporary and local. It is highly
unlikely that the small area affected by the increased
turbidity caused by disposal operations can have more than a
negligible effect on the total estuarine phytoplankton
primary production (Flemer, 1970) .
2. Zooplankton
The temporary and local nature of the turbidity plume
associated with dredged material disposal (see Appendix D)
limits any effect upon zooplankton to a small area. Estuarine
zooplankton must already be adapted to coping with levels of
suspended sediment similar to those found over much of the
excess turbidity plume from dredged material disposal (Goodwyn,
1970) .
3. Nekton
The generally small area that is temporarily affected by
excess turbidity during dredged material disposal can have no
more than a negligible effect on nekton populations in the
estuary (Dovel, 1970) .
4. Benthos
The generally small area that is temporarily affected by
excess turbidity during dredged material disposal can have no
more than a negligible impact on benthic populations outside
of the immediate disposal area (Pfitzenmeyer, 1970).
121
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5. Fish Eggs and Larvae
Numerous studies (Schubel and Wang; 1973, Sherk et al.;
1970, Auld and Schubel; 1978) have indicated that the survival
of eggs and larvae of typical estuarine fishes (yellow perch,
blueback herring, alewife, American shad, white perch, striped
bass) are not significantly decreased by exposure to suspen-
sions of natural fine-grained relatively uncontaminated
sediments with concentrations much greater than those typi-
cally observed, even during dredging and disposal. Based on
these studies we conclude that the excess concentrations of
suspended sediment that result from dredging and disposal of
relatively uncontaminated sediments do not represent a
significant hazard to fish eggs and larvae as far as acute
effects are concerned. Chronic effects have, however, not
been adequately investigated.
P.eferenzes
Auld, H.K. and J.R. Schubel. 1978. Effects of suspended
sediment on fish eggs and larvae: a laboratory assessment.
Est. Coast. Mar. Sci. 6:153-164.
Flemer, D.A. 1970. Project B, Phytoplankton. Pages 16-25
-in Gross physical and biological effects of overboard spoil
disposal in upper Chesapeake Bay. Natural Resources
Inst., Special Rept. #3, Ches. Biol. Lab., Univ. of Md.
Goodwyn, F. 1970. Project D, Zooplankton. Pages 39-41 in
Gross physical and biological effects of overboard spoil
disposal in upper Chesapeake Bay. Natural Resources
Inst., Special Rept. $3, Ches. Biol. Lab., Univ. of Md.
Pfitzenmeyer, H.T. 1970. Project C, Benthos. Pages 26-38
in Gross physical and biological effects of overboard spoil
disposal in upper Chesapeake Bay. Natural Resources Inst.,
Special Rept. #3, Ches. Biol. Lab., Univ. of Md.
Richie, D.E. 1970. Project F, Fish. Pages 50-63 in Gross
physical and biological effects of overboard spoil disposal
in upper Chesapeake Bay. Material Resources Inst., Special
122
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Rept. #3, Ches. Biol. Lab., Univ. of Md.
Schubel, J.R. and J.C.S. Wang. 1973. The effects of sus-
pended sediment on the hatching success of Pe^oa, ?lc,vescer,s
(yellow perch) , Morone zrr.e?icar.z (white perch) , Xo?one
saxa-ilis (striped bass) and Atosa pseudckz?engus (alewife)
eggs. Special Rept. #30, Chesapeake Bay Inst., Johns
Hopkins University, Ref. 73-53, 77pp.
Sherk, J.A. and L.E. Cronin. 1970. the effects of suspended
and deposited sediments on estuarine organisms. An annotated
bibliography of selected references. Univ. of Md., National
Res. Inst., Ref. 70-19, 61pp + Addendum.
123
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APPENDIX H
cf benthos by disposal a~t proposed sl~es
cf ^na-erlals dredged f?orr. zhe Chesapeake and
Delaware Canal Approach Channel (Table 4b).
At the submarine disposal sites considered in this
section smothering of benthos by the disposal of dredged
material will probably be complete. Recolonization will
occur relatively rapidly, however (see Appendix P).
The trough has a lower density and a lower diversity of
benthic organisms than the overboard area adjacent to the
Chesapeake and Delaware Approach Channel. The benthic
assemblage in the trough is essentially eliminated every
summer by the anoxic, or nearly anoxic, conditions that
characterize its near-bottom waters (H. Pfitzenmeyer,
Personal Communication, 1980) .
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APPENDIX I
Zxc lusi on/Ar- traction of Fish at C & D
Approaches Alternatives (Table 4"o) .
During disposal operations attraction of local finfish
to the turbidity plume has been occasionally observed. This
attraction has been attributed to releases of particulate
organic matter associated with the dredged material which
serve as a food source for the fish. Finfish have also been
observed to be repelled by the turbidity plume, perhaps in
response to the generally lowered dissolved oxygen levels in
its immediate vicinity. Generally it has been observed that
fish are more sensitive to oxygen depletion than to excess
turbidity, and appear to be repelled from the disposal area
before encountering the high turbidity levels located within
the plume. Because of this defensive mechanism, and also
because of the limited area strongly affected by increased
turbidity during disposal (see Appendix D), disposal opera-
tions do not pose a threat to resident finfish populations
at locations where sufficient space is available to enable
fish to avoid the plume. This is true for all the locations
under consideration in this report.
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APPENDIX J
Uptake of contaminants by biota during t'ne disposal
of Chesapeake and Delaware Canal Approach Channel
materials at proposed disposal sites (Table 4b).
1. Metals
Because the release of soluble metals during disposal
operations is considered unlikely (see Appendix E), uptake
of metals by benthos, plankton, and nekton at either dis-
posal location will be negligible.
2. CHCs
Because the release of soluble CHCs during disposal is
considered possible (see Appendix E), their subsequent uptake
by benthos, plankton, and nekton is possible at either
disposal location.
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APPENDIX K
Excess turbidity in water column subsequent to
disposal of material dredged from the
Chesapeake and Delaware Canal Approach Channel
(Table 4b).
Potential environmental impacts of excess turbidity
resulting from resuspension of sediment from dredged material
piles include the reduction in the penetration of sunlight,
clogging of filter feeding benthos and nekton with excess
sediment, and interference of movement of nekton. Concern
about these possible effects arises because for some period
after disposal, material in the disposal pile is more suscep-
tible to resuspension than the surrounding bottom, and could
become a persistent local source of excess turbidity.
Immediately after disposal, a dredged material pile
contains significantly (% 20%) higher amounts of pore water
than the surrounding, naturally deposited, sediments. This,
combined with its positive relief, makes the disposal pile
more susceptible to disturbance by wind waves and tidal
currents than the surrounding bottom. The possible signifi-
cance to the biota of this added source of turbidity and
suspended sediment must be put into perspective in assessing
its possible environmental and ecological effects by consider-
ing (1) the point of introduction of this turbidity relative
to the location of the important organisms in the disposal
area, and (2) its magnitude relative to natural variation
in turbidity at the particular disposal site.
Although the dredged material pile has positive relief,
its height composes a small to insignificant fraction of the
water column at either disposal location (see Appendix 0).
A 1.5 m high mound in the disposal area in the upper Bay
represents about 25% of the average water depth and less
than 5% of the water depth in the trough. The point of
introduction of any excess turbidity is therefore essentially
127
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the same as that for the surrounding water—the ambient Bay
bottom. Observations of the periodic resuspension of bottom
sediment in the Chesapeake Bay (Schubel, 1972) by tidal
currents show that the effect of excess turbidity usually
reaches no closer than within 2 m of the water surface in the
upper bay and no closer than 20 in of the surface in the trough
of the middle Bay. There is no reason to suspect that the
dredged material would be resuspended significantly higher
into the water column than sediments naturally accumulating
on the surrounding bottom since their textures are similar
(Table 2). Examination of the typical euphotic depths
(Table 3) in the potential disposal areas suggests that
resuspension of dredged materials would have little effect
on primary production.
The shallow and variable euphotic depths in the
Chesapeake Bay are the result of persistent and variable
natural turbidity. Organisms adapted to migrating through
the Bay (nekton)_, and living on its bottom (benthos) , must be
accustomed to these conditions. Although it is impossible to
accurately predict what the magnitude of excess turbidity at
the disposal sites would be, it is unlikely that significant
excess turbidity could be generated for a prolonged period
of time. As the more readily erodable fractions are removed
and as the pile consolidates, an equilibrium of erosion
resistance will be reached. If the location is carefully
chosen so as to minimize turbulence, desirable for other
reasons as well (see Appendix L), excess turbidity will be
minimized.
Because of the high and variable natural levels of
turbidity at the disposal sites under consideration in this
section, we consider any excess turbidity generated by the
disposal pile to be negligible.
128
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Reference
Schubel, J.R. 1972. Distribution and transportation of
suspended sediment in upper Chesapeake Bay. Pages 151-167
•in Geol. Soc. Am. Memoir #133 P:151-167.
129
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APPENDIX L
Evaluation of possible contaminant releases to
tiater column subsequent to disposal of material
dredged from Chesapeake and Delaware Approach
Channel at various disposal options.
1. Metals (Table 4b)
Most of the metals of environmental concern are bound to
sedimentary particles as reduced compounds. The solubility
of these compounds is determined mostly by the dissolved
oxygen level of the water in immediate contact with the
particles. Strategies for keeping sediment-associated metals
within the dredged material pile should maintain the reducing
character of the sediment's interstitial waters. Geochemical
theory indicates that the release of metals subsequent to
disposal by chemical solubilization is unlikely if the reduc-
ing character of the pore waters is maintained.
The vast bulk of all sediment contained within the
disposal pile will be surrounded by its own interstitial
waters; only a thin surface layer will be in contact with
overlying waters. In fine-grained estuarine sediments typi-
cal of the dredged materials considered here, pore waters
develop a chemical micro-environment determined largely by
the interaction of various sediment-associated constituents,
principally organic compounds, and their sulfur-containing
degradation products. The conditions of this environment
approach an oxygen free state indicating the large capacity
of the sediments to sequester oxygen. Under these conditions,
the formation of reduced insoluble sulfur-metal compounds is
favored, and most metals, with the exception of iron and
manganese, become bound to the sediment as insoluble sulfides.
Iron and manganese, which form soluble reduced compounds in
the interstitial waters, migrate to the top of the sediment
pile and have been shown to diffuse into the near-bottom
waters. This is a natural process that is widespread in
130
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estuaries containing fine-grained sediment (Matisoff et al.,
1975), (Turekian, 1977) .
There are no data to suggest that once compaction of the
spoil pile is complete the diffusive flux of iron and manganese
to the overlying waters will be either enhanced or retarded
relative to the natural rate before dredging and disposal.
This is because a principal determinant of the diffusivity
of the pore waters, the sediment grain size, will be unchanged
(see Table #2). The possibility exists that during a period
of several months after disposal the expulsion of sediment
pore waters from the sediment pile will enhance the flux of
dissolved Fe and Mn (and nutrients) to the near bottom waters.
As calculated in appendix m, compaction of a disposal pile
S3 /r -3
containing 0.75 x 10 m (1 x 10 yds ) of dredged material
9
will release 1.8 x 10 g of pore waters. If these contain
100 PPM Mn (average values for Chesapeake Bay Sediments),
1.8 x 10 g of soluble Mn are released. This is almost
certainly an over-estimate since a significant fraction of
this Mn will precipitate as insoluble hydroxides on the sedi-
ment water interface, and will not be dissolved. If this
were to totally dissolve into the waters of the upper Bay
(% 3.8 x 10 1}, it would result in a Mn concentration of
— 8 —5
4.7 x 10 g/£ or 4.7 x 10 PPM—an undetectable increase.
If this amount were to be dissolved into a disposal area of
22
2.56 km (1 mi ) with an average depth of 3.5 m (10 ft), the
increase in the concentration of Mn would still be only
1.9 x 10~5 g/£ or 1.9 x 10~2 PPM.
Geochemical theory indicates that the sequestering of
metals within the disposal pile will be complete if reducing
conditions are maintained. Observations of turbulence and
sediment resuspension at the two locations under consideration
as disposal sites indicates that the disposal pile would be
less likely to be disturbed in the deeper waters of the trough
south of the Bay Bridge at Annapolis. For this reason, the
trough is preferable with regard to the long term sequestering
of metalso Release of metals from sediment disposed in the
upper Bay is, however, also unlikely.
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The extent of contamination of the sediments naturally
accumulating in the northern Chesapeake Bay, including those
in the C & D Approach Channel, is determined by an equilibrium
between the sediment sources, mostly the Susquehanna River,
and the physico-chemical conditions found at the site of
deposition. Because the bottom waters in the upper Bay are
more turbulent and more highly oxygenated than they are in
the trough site, materials accumulating in the Chesapeake
and Delaware Approach Channel have already adjusted to
conditions less favorable to the retention of metals than are
found in the trough south of the Bay Bridge at Annapolis.
The geochemical equilibria that control metals solubility in
a sediment column favor retention of metals in the bottom
sediments of the upper Bay and are even more favorable in
the trough.
2. Nutrients
The processes that control the rate of nutrient regenera-
tion from sediments are the rate of bacterial decay of organic
matter in sediments, the grain size of the sediments, the
rate of physical and biological reworking, and the sedimenta-
tion rate. Nutrient profiles in the pore waters of undis-
turbed sediments develop in response to an equilibrium
between the diffusional flux and the rate of production at
depth. Benthic regeneration of nutrients is an important
natural process that supplies a large portion of the nutrients
required for primary production in many estuaries. As with
similar arguments made under part (1) of this appendix for
dissolved iron and manganese, there is no reason to believe
that the regenerative flux of nutrients (NOT, P0~, NH_) from
the dredged material pile will be different from that natu-
rally occurring in the sediments around the pile, after
compaction of the pile has taken place. During the compac-
tion process, the fluxes of nutrients will be enhanced. The
magnitude of enhancement can be placed into perspective by
comparing it with the natural nutrient regeneration rate.
Ammonia, as NH4 is the principal species of dissolved
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nitrogen in reducing sediments which contain an average of
2-3 ra mol NH.. Typical NH, regeneration rates from fine-
21
grained reducing sediments average 872 y mol/m /d (Bartwig,
1976). The compaction of 0.8 x 106m3 of (1 x 106yd3) of
c
dredged material will release 1.8 x 10 I of pore waters over
a period of about a year. This results in a flux of NH, to
3 ^
the overlying water of 5.4 x 10 moles of NH,. The amount
of NH4 added to the water column by fine-grained sediments
in the upper Bay (worst case, minimum area) is the area of
6 2
the upper Bay (814 x 10 m Turkey Point to Mouth of Patapsco
River without tributaries) multiplied by the average regenera-
— 62 8
tion rate (872 x 10 m/m /d) which gives 2.6 x 10 moles
NH. per year. Five orders of magnitude more NH. is regenerated
each year naturally to the upper Bay than would be contributed
by expulsion of pore waters from dredged materials.
3. Chlorinated Hydrocarbons
Although these substances may have a greater potential
to impact the marine ecosystem than any of the contaminants
previously described, relatively little is known about their
geochemical behavior. In part this is because chlorinated
hydrocarbons have only recently been recognized as serious
pollutants and research results are only beginning to be
synthesized. Lack of information is also due to the analyti-
cal difficulties these diverse compounds present; much of
the earlier work on the environmental chemistry of CHCs must
be considered unreliable because of analytical uncertainty.
The combination of high toxicity at low concentrations and
analytical difficulty makes research both difficult and
necessary. At the present time statements about the long
term geochemical behavior of chlorinated hydrocarbons cannot
be made with the same degree of confidence as similar state-
ments made in this report about metals.
A "worst case" analysis may be made by determining the
levels of dissolved chlorinated hydrocarbons that would
result from dissolution from dredged material into the over-
lying waters in various parts of the Chesapeake Bay using a
133
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4
portion coefficient of 10 . As calculated from values in
Table #2, 1 x 10 metric tons of sediment dredged from the
5 4
C & D Approach Channel contains 9 x 10 g PCS and 2 x 10 g
DDT. The dissolved levels resulting from the dissolution of
this material to equilibrium with the overlying waters at
the two disposal sites are shown in the table below. The
volumes of the Bay used in the calculation are, for the
northern disposal site (overboard) from Turkey Point to the
mouth of the Chester River, and from the Lane Bridge at
Annapolis to Sharps Island for the proposed trough disposal
site.
Disposal Area Volume PCS*
Overboard
Trough
3827 x 106m3
8806 x 106m3
0.02 x 10"4
0.01 x 10~4
5 x 10~9
2 x 10"8
*Dissolved levels in PPM resulting from total dissolu-
tion from dredged material (1 x 10s tons).
Ninety g of PCB and 2 g of DDT would be released. This
should be compared with the estimated input of PCBs from the
Susquehanna River to this region of 506 kg/y (Munson, 1975),
most of which is bound to suspended sediment. The releases
from dredging and disposal, depending upon the season, might
be more available for biological uptake than the river sup-
plied material however.
References
Matisoff, G., O.P. Bricker, G.R. Holdren and P. Kaerk. 1975,
Spatial and temporal variations in the interstitial water
chemistry of Chesapeake Bay sediments. Pages 343-363 in
T.M. Church, ed.f Marine Chemistry in the Coastal Environ-
ment. A. C. S. Symp. Ser. #18.
Berner, R.A. 1972. Principles of Chemical Sedimentology.
McGraw Hill Pub. 239pp.
134
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Stumm, W. and J.J. Morgan. 1970. Aquatic Chemistry. Wiley
Interscience Pub. 583pp.
Turekian, K.K. 1977. The fate of metals in the oceans.
Geochem. Cosmochem. Acta. 41:1139-45.
Munson, T.O., D.D. Ela, and C. Rutledge Jr., eds. 1975.
Upper Bay Survey, Final Report to the Department of Natural
Resources, V.II. Westinghouse Electric Corp., Oceanic
Division, Annapolis, Md.
Matisoff, G., O.P. Bricker, G.R. Holdren, and P. Kaerk.
1975. Spatial and temporal variations in the interstitial
water chemistry of Chesapeake Bay sediments. Pages 343-363
in F.K. Church, ed., Marine Chemistry in the Coastal Environ-
ment. A. C. S., Washington, D.C.
135
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APPENDIX M
Evaluation of possible oxygen depletion of the
uater column subsequent to disposal of material
dredged from the Chesapeake and Delaware Canal Approach
Channel under various disposal options (Table 4e).
The main source of oxygen demand exerted by the dredged
material pile upon the overlying water over and above the
normal oxygen demand of the sediments at the disposal site
results from the gradual expulsion of reduced pore waters
under the influence of gravitational compaction. During the
hydraulic or hopper dredging/disposal process, water content
of the dredged material is increased by approximately 20% by
mass. Subsequent to disposal, gravitational compaction
gradually expels this water, probably over a period of years.
For 0.75 x 106m3 (1 x 106 yd3) of dredged material (9.18 x
9 3
10 g of sediment plus water with a mean density of 1.2 g/cm ),
Q
compaction of ^ 20% results in the expulsion of 1.8 x 10 g
H90. The typical oxygen demand of highly reducing pore
= -3 -2
waters (HS concentration % 7 x 10 moles/Jl) is 1.5 x 10
moles 02/£ (Schubel et al., 1978). If all the pore water
were expelled at once, it would produce an oxygen demand of
8.6 x 105 g 02 (2.7 x 104 moles).
In the summer, oxygen levels in the deep trough drop
below 1 yg/g. Since the volume of the deep hole below 20 m
is about 528 x 10 cm , it might contain 5.2 x 10 g 02—
almost an order of magnitude more oxygen than is required to
satisfy the oxygen demand of the pore water assuming it were
all expelled at once and there was no mixing with the over-
lying waters. During most of the year, dissolved oxygen
levels in the trough are closer to 5 ug/g which would provide
2.6 x 10 g 0-—more than two orders of magnitude more than
required to satisfy the total oxygen demand of the pore
waters under worst case conditions.
In reality the expulsion of reduced pore waters occurs
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at a very slow rate, and the expelled water is rapidly mixed
with the overlying waters so that the immediate oxygen demand
would not produce a detectable oxygen sag in the near-bottom
waters of the trough. Similar arguments can be made for the
more highly oxygenated waters of the upper Bay.
Reference
Schubel, J.R., H.H. Carter, R.E. Wilson, W.M. Wise,
M.G. Heaton, M.G. Gross. 1978. Field investigations of
the nature, degree, and extent of turbidity generated by
open-water pipeline disposal operations. Technical Kept.
D-78-30 U.S.A.C.E. Dredged Material Research Program.
137
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APPENDIX N
Movement of materials dredged from Chesapeake
and Delaware Canal Approach subsequent
to disposal at various sites (Table 4a).
Substantial movement of disposed dredged materials out-
side the designated disposal area is a perceived environmental
hazard to commercially important benthic organisms, particu-
larly oysters. Large scale movement may be the result of two
processes:
Fluid flow of sediment which may occur immediately
after disposal and
Resuspension of sediment and transport by advective
and diffusive processes—a process which may occur
over a long time period.
Biggs (1970) monitored the disposal and ultimate fate
of dredged materials discharged into the upper bay overboard
site in 1967. He found that the dredged material pile-
immediately after disposal had an average slope of 500:1 and
an average height of 1.5 m. An area at least five times that
of the intended disposal site was covered by "fluid mud flow"
and < 90% of the total volume of material dredged could be
accounted for within the pile five months after disposal.
The long term effect of sediment resuspension on this pile
remains unevaluated.
The physical and bathymetric characteristics of a
disposal site in the trough below the Bay Bridge place limits
on the extent of migration of the dredged materials subsequent
to disposal. In contrast to the upper Bay disposal area,
which is shallow and has relatively little relief, the middle
Bay site is at the bottom of a deep trough. Fluid flow of
the material disposed in the trough will be limited by the
sides of the trough. There is no possibility that this mate-
rial could flow out of the trough and impact the oyster bars
near its margins. Also the decreased turbulence (Appendix A)
138
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at this site makes long-term resuspension (Appendix B) less
likely than in the upper Bay.
Reference
Biggs, R.B. 1970. Project A, Geology and Hydrography. Pages
7-15 in Gross physical and biological effects of overboard
spoil disposal in upper Chesapeake Bay. Natural Resources
Inst., Special Rept. 13, Ches. Biol. Lab., Univ. of Md.
139
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APPENDIX 0
Effect of changes of bottom topography from
disposal of materials dredged from the Chesapeake
and Delaware Canal Approach Channel (Table 4c),
Significant alteration of bottom topography by the
creation of dredged material mounds could affect circulation
in the disposal area and also interfere with the activities
of commercial drift net fishermen. The extent of such
effects can be predicted by considering the reduction of
bay cross sectional area caused by the disposal process and
the geometry of the disposal mounds.
In the upper Bay the average height of the dredged
material pile created during disposal activities in 1967
(Biggs, 1970) was 1.5 m. Although this is about 25% of
the depth in this area (4 to 6 m) the reduction of cross
sectional area is very small because the disposal pile runs
roughly parallel to the axis of the Bay. The dimensions of
this pile are = 100 m wide x 3 km long x 1.5 m high and it
has no measurable effect on circulation. If it interferes
with drift nets used by commercial fishermen in this area,
the relief of the pile could probably be reduced during
disposal, or afterward, by drag-line operations. Such an
operation, however, would remove a principal advantage of
creating a pile, the minimization of exposed sediment sur-
face area, which limits the release of contaminants (see
Appendix L).
In the trough the much greater depth (average depth
ty 31 m) virtually precludes any measurable effects on circu-
lation. The volume of the trough from 20 m to the bottom in
this area is 528 x 10 m . This should be compared with the
total projected volume of dredged material for the next twenty
years in the Maryland portion of the Bay of 50 x 10 m .
Disposal of all this material within the trough could not be
140
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expected to produce a measurable effect on circulation in
this area (Schubel and Wise, 1979).
References
Biggs, R.B. 1970. Project A, Geology and Hydrography.
Pages 7-15 in Gross physical and biological effects of
overboard spoil disposal in upper Chesapeake Bay. Natural
Resources Inst., Special Rept. #3, Ches. Biol. Lab., Univ.
of Md.
Schubel, J.R. and W.M. Wise, eds. 1979. Pages 90-94 in
Questions About Dredging and Dredged Material Disposal in
the Chesapeake Bay. Special Rept. 20, Marine Sciences
Research Center, State University of New York.
141
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APPENDIX P
Time for recovery of "oenthic communities subsequent
to disposal operations at sites under consideration
for the disposal of material dredged from the Chesapeake
and Delaware Canal Approach Channel (Table 4c),
1. Biomass
A possible significant effect of dredged material dis-
posal is the long term destruction, by burial, of benthic
communities which serve as a food resource for many commer-
cially important fishes. Studies of the recovery of the
benthic communities on dredged material piles have been made
in upper Chesapeake Bay, following overboard disposal of
material dredged from the C & D Approach Channel in 1967
(Pfitzenmeyer, 1970), and in Long Island Sound at a deep
(20 m) disposal site for materials dredged from New Haven
Harbor (Rhoads et al., 1978), and in other areas.
Pfitzenmeyer (1970) studied the changes in benthic bio-
mass (mass of organisms/mass of sediment) caused by overboard
disposal of material dredged from the Chesapeake and
Delaware Approach Channel. An immediate decrease of 64% in
the dry biomass was followed by an 85% increase in biomass
within four months of disposal. This was in turn followed
by a lesser increase over the next six months. During the
same period, the number of individuals represented by this
biomass fluctuated widely, apparently following a natural
cycle keyed to salinity variations in the overlying waters.
Within a year and a half there was no apparent difference
between the predisposal and post-disposal communities, as
measured with standard parameters and compared with normal
variation outside the disposal area.
The Long Island Sound Disposal Site studied by Rhoads
et al. (1978) is a deep, relatively quiescent area similar
in some respects to the mid-Chesapeake Bay trough. At that
site, relatively contaminated material from New Haven Harbor
142
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was discharged by hopper barge. the immediate recruitment of
organisms on the pile was slower than at nearby control areas,
suggesting inhibition by toxic substances released from the
pile. Relatively contaminated dredged material was covered
with a thin layer of "cleaner" material obtained during the
dredging of less contaminated areas of the harbor. Recovery
of benthic community biomass at the disposal site subsequent
to disposal was at first extremely rapid. The initial
increase in biomass was followed by a decline which was
related to ecological conditions at the disposal site.
Within one and a half years the density of organisms on the
surface of the dump site had recovered to within the range
of apparent variability of the surrounding bottom. This
variability is probably due to a combination of factors
including large changes in planktonic recruitment, inter-
species competition, and the possible effect of sediment
contaminants.
Changes in benthic communities due to dredged material
disposal should be evaluated in comparison with the normal
large, natural variability which results in response to
complex and often unknown factors that characterizes the
natural bottom. In the northern Chesapeake Bay bottom-
dwelling organisms are frequently subject to environmental
"catastrophes" unrelated to man's activities, storm and
floods. The benthic community in the trough is also subject
to periodic mortality in summer due to depression of dis-
solved oxygen to near zero levels.
Studies show that total biomass is not significantly
affected by dredged material disposal in areas similar to
the Chesapeake Bay.
2. Diversity
Diversity is a measure of the complexity and variety of
an ecosystem and is strongly affected by the degree of environ-
mental variability encountered by the community. A high
degree of diversity is thought by ecologists to be the result
of continued stability of the environment for a prolonged
143
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period, allowing complex interrelationships to be developed
among organisms.
The two disposal sites under consideration in this case
are quite different in the degree of environmental variability
encountered by the benthic community. This is perhaps not
fully reflected in the parameters stated in Table 3 because
of extreme episodic nature of some of the changes. Salinity,
for example, in the upper reaches of the Bay drops to zero
for a period of several weeks during the annual Susquehanna
freshet. Aperiodic large floods carry tremendous quantities
of sediment to this area, burying the bottom fauna. While
salinity of the mid-Bay trough site is variable, it rarely,
if ever, drops to zero and variability in sediment input is
greatly reduced this far from the Susquehanna River—the
principal source of fluvial sediment.
Disposal of dredged materials in the upper Bay is
another variable "event" covering a small area in addition
to many natural changes. Because the benthic community in
this area has a low diversity index to begin with
(Pfitzenmeyer, 1970), changes caused by dredged material
disposal are small and readjust rapidly. Subsequent to dis-
posal of dredged material at the upper Bay location in 1967,
the diversity index of benthic organisms in the disposal
area dropped. Complete recovery of the benthic community
to predredging levels was observed within one year.
This was not the case for the disposal of dredged
material in Long Island Sound; a much more stable environ-
ment populated by a mature benthic community. Here even
several years subsequent to disposal, the benthic community
at the disposal site was still significantly less diverse
than that of surrounding bottom (Rhoads et al., 1978). The
near-bottom environment in the Chesapeake Bay trough site is
more variable than that in Long Island Sound. No information
on the structure of the benthic community in the Chesapeake
Bay trough is available. Until this information is obtained,
ecological studies in other areas suggest that recovery of
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species diversity of the benthic community in the trough to
predisposal levels would probably be similar to, or more
rapid than in the upper Bay. The diversity of the benthic
assemblage in the trough is almost certainly lower than that
in the overboard disposal area in the upper Bay. The benthic
organisms in the trough are eliminated, in all likelihood,
every summer when the oxygen content of near-bottom waters
falls to near zero levels.
The possible ecological effect that alterations in the
benthic community might have on the nekton remains unevaluated,
but probably is small. Considerable controversy exists regard-
ing the species characteristics of the most productive benthic
communities. Some authors suggest that dredging affected
communities may be even more productive than undisturbed
bottoms (Rhoads et al., 1978) because of the sudden explosive
increase in biomass associated with the recruitment of
opportunistic species. It remains unclear whether these
organisms are necessarily readily utilized as food by higher
trophic levels (nekton). The areas of Chesapeake Bay,
affected by dredged material disposal are a fraction of the
total area and probably do not have a measureable effect on
higher trophic levels because of alterations in the benthic
community structure. Studies of the benthic community of
the trough should be made. This is essential if the trough
is to be considered as a potential site for disposal of
dredged material.
References
Pfitzenmeyer, H.T. 1970. Project C, Benthos. Pages 26-38
in Gross physical and biological effects of overboard
spoil disposal in upper Chesapeake Bay. Natural Resources
Inst., Special Rept. #3, Ches. Biol. Lab., Univ. of Md.
Rhoads, D.C., P. McCall, J.Y. Yingst. 1978. Disturbance
and production on the estuarine sea floor. American
Scientist 66:577-583.
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APPENDIX Q
Uptake of sontam-i.na.nts by organisms at the proposed
disposal sites for materials dredged from the Chesapeake
and Delaware Canal Approach Channel (Table 4o).
A. Metals
1. Benthos. Benthic organisms living in or on the
sediment ingest sediment particles as part of their regular
feeding activities. The characteristics of the digestive
tracts of these organisms are such that dissolution and
uptake of metals from sediments may occur. Although benthic
organisms must be adapted to sediment-associated metals at
natural levels, added anthorpogenic loadings may be in
chamical forms more easily desorbed which may cause deleter-
ious effects to the benthos themselves, or may be concentrated
higher in the food chain. Benthic organisms, low in the
trophic structure of marine ecosystems, may provide the
entry point into biological cycles for the otherwise gener-
ally unavailable metals.
Although many experiments on the effects of increased
metals concentrations on benthic organisms have been performed,
most of the data generated are of little value in predicting
the environmental effects of metal loadings in dredged sedi-
ments. Host studies have utilized soluble metals at far
higher concentrations than those found in the environment.
In studies of sediment uptake, many investigators have failed
in their analyses to differentiate between sediment-associated
metals in the digestive tract and metals that have been
incorporated into the organism's tissues.
We have very limited ability to predict the effects of
sediment-associated metals on the benthos or on higher
trophic levels. Experiments (Bryan and Hammerstony, 1973a,b;
Shuster and Pringle , 1968) have demonstrated that uptake
of metals by Crustacea, polycheates, and mollusks is possible.
A conservative criterion at this time is to restrict disposal
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to materials whose metals concentrations are at or below
those in the proposed disposal area to minimize the elevation
of these contaminants at the disposal site. The sites chosen
to receive the dredged materials under consideration in this
report have been chosen using this criterion.
2. Plankton. Because the release of soluble (see
Appendix L) metals from the disposal pile is negligible,
uptake of metals by plankton is unlikely.
3. Nekton. Uptake of metals by nekton results
principally from ingestion of dissolved metals and contam-
inated benthic or planktonic organisma.
B. CHCs
Because long-term desorbtion of chlorinated hydrocarbons
from the disposal pile is considered a possibility (Appendix
L) and these substances are known to be taken from solution
by plankton (H.B. O'Connors, personal communication, 1979) ,
mollusks (Duke et al., 1970), and nekton (Smith and Cole,
1970), uptake of CHCs by these organisms cannot be discounted.
Careful comparisons between the CHC content of the dredged
material and the sediments of the disposal area should be
made.
References
Bryan, G.W. and L.G. Hammerstony. 1973a. Adaptation of the
polychaete Here-is devers-ieolor to manganese in estuarine
sediments. Journal of the Marine Biological Association
of the United Kingdom. 53:859-872.
Duke, T.W., J.I. Lowe, and A.J. Wilson, Jr. 1970. A poly-
chlorinated biphenyl (Aroclor 1254) in water, sediment, and
biota of Escambia Bay, Florida. Bull, of Environmental
Contamination and Toxicology. 5(2):121-180.
Schuster, C.N., Jr. and B.H. Pringle. 1968. Effects of
trace metals on estuarine mollusks. Prod., 1st Mid-Atlantic
Industrial Waste Conf., Univ. Delaware. CE-5:285-304.
147
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Smith, R.M. and C.F. Cole. 1970. Chlorinated hydrocarbon
insecticide residues in winter flounder, Pseudopleuronectus
amer-i-octnus, from the Weweantic River Estuary, Massachusetts,
J. of the Fisheries Res. Bd. of Canada. 27(12)2374-2380.
148
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APPENDIX R
Frequency of maintena.noe dredging of
Baltimore Harbor Approach Channel as affected by
utilization of various disposal options (Table 7).
If dredged materials are not removed sufficiently or
isolated from the dredging site, resuspension by waves and
_tidal currents, and mass movements may cause the return of
these materials to the channel. Since most material dredged
previously from Baltimore Harbor Approach Channels has been
disposed overboard, continued utilization of this option
will not result in any change in the historical frequency of
dredging required to maintain the channel. Confinement of
dredged material, or utilization of more removed sites,
could be expected to decrease the frequency of maintenance
dredging required.
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APPENDIX S
Degree of t^rbulenoe at disposal sites proposed for1 materials
dredged from the Baltimore Harbor Approach Channels (Table ").
As previously discussed (Appendix A), secondary sources
of turbulence in addition to tidal stresses are probably the
cause of significant differences in the turbulence of near
bottom waters at various locations in the open Chesapeake Bay.
These secondary sources, wind waves and the wakes of ships,
have a surface origin and are therefore depth dependent.
The undiked overboard option is considered most turbu-
lent because of its shallowness and proximity to frequent
ship traffic. It is also exposed significantly to the effects
of wind generated waves. Diking of this site with structures
that approached the water surface would reduce the effects of
surface waves significantly. The two other sites, near Kent
Island and in the deep trough, are significantly deeper and
removed from the effects of surface waves. Fringing wetland
areas which are alternately submerged and exposed by the tides
are subject to turbulent stress from tidal currents and wind
waves. Once vegetated, the plants are effective in stabiliz-
ing the bottom.
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APPENDIX T
Intensity of sediment resuspension at disposal-
sites proposed for materials dredged from Baltimore
Harbor Approach Channels (Table 7),
Bottom sediment resuspension results from turbulent
stresses exerted by near-bottom waters on the surficial sedi-
ments. It is greatest where shear stresses are high and
shear strengths (critical erosion speeds) of the sediments
are low. Without additional information on the physical and
biologically-mediated sediment characteristics (Appendix B)
that determine the critical erosion speed of sediments at
the various disposal sites, we assume the velocities required
for resuspension are similar. All sites are characterized by
fine-grained materials of similar texture. The amount of
sediment resuspension of the various sites is therefore con-
sidered only as a function of water turbulence, and the sites
are ranked accordingly.
The shallow overboard site is similar to the upper Bay
site in this regard and is ranked most turbulent with most
sediment resuspension. Diking of this site would probably
reduce significantly the effect of wind waves, ship wakes,
and tidal currents with a consequent reduction in sediment
resuspension if the dikes approached the water surface. The
Kent Island and deep trough sites are less susceptible to
resuspension than the undiked overboard option because their
greater depth limits disturbance of the bottom by waves.
Once fringing areas are vegetated, roots stabilize the sedi-
ments and the plant stems dissipate wave and current energy.
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APPENDIX U
Excess turbidity in vater column during disposal
at disposal sites proposed for materials dredged
from Baltimore Harbor Approach Channels (Table 3a).
The origin and extent of excess turbidity generated dur-
ing disposal by the methods under consideration have already
been discussed in detail in Appendix D. The conclusion
stated there that excess turbidity during disposal is tempo-
rary and local in extent, holds for the sites under
consideration in this section.
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APPENDIX V
Contaminant releases to water column during disposal
operations at disposal sites proposed for materials
dredged from Baltimore Harbor Approach Channels (Table 3a).
The possible release of contaminants from dredged mate-
rials during disposal operations is determined, in decreasing
order of importance, by (1) the geochemical characteristics
of the dredged materials, (2) the method of disposal, (3) and
the physical conditions at the disposal site. Because the
essential geochemical characteristics of the sediments under
consideration in this section from the Baltimore Approach
Channels (fine-grained, high organic content, reducing
character) are the same as those of the C & D Approach Channel
material, the detailed arguments of Appendix E are equally
applicable here. Further, the physical characteristics of
the water column at the locations under consideration in
this section are not significantly different from those in
the previous section. For these reasons, the conclusions
expressed below are the same as those in the previous section
and referred to Appendix E.
1) Metals
The possible release of metals from dredged materials
during disposal operations of the type considered here has
been discussed in detail in Appendix E. The conclusion,
that any release is negligible, holds for these locations.
2) Nutrients
The release of nutrients by the expulsion of inter-
stitial waters from material during disposal operations has
also been considered in detail in Appendix E. The conclusion,
that such release will have a negligible impact on the water
column, is equally valid for the sites under consideration
here.
3) CHCs
The conclusion expressed regarding the possible release
153
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of CHCs during disposal in Appendix E must be considered
applicable to these sites as well in the absence of a solid
geochemical understanding of these complex substances. The
conflicting data about their potential for release from sea:
ment requires that the possibility of such release is not
excluded.
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APPENDIX W
Oxygen depletion of water column during disposal
operations at disposal sites proposed for materials
dredged from Baltimore Harbor Approach Channels (Table 3a).
As discussed in detail in Appendix F, oxygen depletion
of the water column during disposal is caused by the presence
of reduced compounds of sulfur in the sediment and _its inter-
stitial waters. Numerous investigations of both hopper and
hydraulic disposal methods in a wide variety of environments
have demonstrated that the spatial and temporal extent of
dissolved oxygen depression is always restricted to the
limits of the turbidity plume. There is no reason to believe
that more significant oxygen depression will occur at the
locations under consideration here. See Appendix F for
references.
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APPENDIX X
Ecological effects of increased turbidity of uater column
associated with the disposal of Baltimore Harbor Approach
Channels materials at various disposal options (Table. 8b).
1. Phytoplankton
As discussed Appendix g, decreases in phytoplankton
photosynthesis resulting from increased turbidity because of
dredging and disposal are temporary and local in extent, and
have negligible ecological effects.
2. Zooplankton
As discussed in Appendix G, the temporary and local
nature of the areas of substantial increases in levels of
excess turbidity generated during disposal make possible
significant effects upon zooplankton very unlikely.
3. Nekton
As discussed in Appendix G, the temporary and local
nature of excess turbidity generated during disposal make
possible significant effects upon nekton populations unlikely,
4. Benthos
The area affected by increased turbidity is sufficiently
small so that the amount of the benthic community affected is
insignificant.
5- Rooted Aquatic Plants
Most of the bottom affected by increased turbidity is
well beneath the euphotic depth and contains no rooted plant
life. Some rooted plants might be affected by construction
of new marshes in fringing areas.
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APPENDIX Y
Smothering of benthos by disposal of Baltimore Harbor
Approaches materials in various disposal options (Table So).
At the submarine disposal sites considered in this sec-
tion smothering of benthos by the disposal of dredged material
will probably be complete. Recolonization will occur rela-
tively rapidly, however (see Appendix GG).
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APPENDIX Z
Exolusion/attraotion of fish at Baltimore
Approaches alternatives (Table 8b).
During disposal operations attraction of local finfish
to the turbidity plume has been occasionally observed. This
attraction has been attributed to releases of particulate
organic matter associated with the dredged material which
serve as a food source for the fish. Finfish have also been
observed to be repelled by the turbidity plume, perhaps in
response to the generally lowered dissolved oxygen levels in
its immediate vicinity. Generally it has been observed that
fish are more sensitive to oxygen depletion than to excess
turbidity, and appear to be repelled from the disposal area
before encountering the high turbidity levels located within
the plume. Because of this defensive mechanism, and also
because of the limited area strongly affected by increased
turbidity during disposal (see Appendix U), disposal opera-
tions do not pose a threat to resident finfish populations
at locations where sufficient space is available to enable
fish ot avoid the plume. This is true for all the locations
under consideration in this report.
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APPENDIX AA
Uptake of contaminants by biota, during the disposal
of Baltimore Harbor Approach Channels material
at various disposal sites (Table 3b).
1. Metals
Because the release of soluble metals during disposal
is considered unlikely, benthos, plankton, and nekton will
not be subject to metals concentrations higher than ambient
and the rate of uptake of metals will not be affected. See
Appendix V for more detail.
2. CHCs
Because the release of soluble CHCs during disposal
operations is considered possible, benthos, nekton, and
plankton might take up these compounds at faster rates and
in greater amounts as the result of disposal. See Appendix
V for more detail.
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APPENDIX BB
Excess turbidity -In water colunn subsequent to disposal
of materials dredged from Baltimore Harbor Approach
Channels az the alternative disposal sites (Table do).
The sources and possible environmental effects of per-
sistent excess turbidity in the water column as the result
of disposal activities have been discussed in Appendix K.
The general conclusion, that the location and strength of
this source of excess turbidity is masked by natural varia-
tions in turbidity at the disposal sites, holds for the deep
trough and Kent Island sites.
This conclusion may not hold for undiked overboard
sites. The shallowness of the area, its fetch, and charac-
teristic tidal currents make sediment resuspension by wind
waves, shipping wakes and tidal currents likely. Although
conditions similar to these are characteristic of the upper
Bay overboard site adjacent to the C & D Canal Approach
Channel, the waters in that area were normally subject to
larger and more rapid natural changes in turbidity. At the
overboard disposal locations for the Baltimore Approach
Channels,, natural variability in turbidity levels is reduced
relative to that of the upper Bay. Organisms migrating
through this area may not be well adapted to cope with high
turbidity levels which could result over a significant area
for months after disposal. We consider the biological
impact to be small, however.
Diking of overboard disposal areas would reduce the
effects of surface waves from wind and ships, as well as
tidal currents, and would minimize sediment resuspension and
eliminate this source of excess turbidity. Diked disposal
in fringing areas, if properly constructed, does not allow
escape of sediment by subaerial erosion processes. Vegeta-
tion of fringing marshlands stabilizes the sediment, and
dampens resuspension and therefore excess turbidity.
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Appendix CC
Contaminant releases to water column subsequent
to disposal of materials dredged for Baltimore
Harbor Approach Channels (Table 8a).
Subsequent to disposal, the most important factors
governing the possible release of contaminants from the
disposal pile are the environmental conditions experienced
by the sediment. As pointed out in Appendix L, the most
important factor in minimizing release of contaminants is
the maintenance of anoxic conditions within the disposal
pile. Physical factors at the site play an important role
in determining geochemical conditions within the pile. The
geochemical effects of waves and currents as agents of sedi-
ment resuspension are to oxygenate the sediment pore waters
and to increase the normally slow rates of molecular diffu-
sion. The result is to enhance the transfer of contaminants
from the sediment to the overlying water.
The submarine disposal options considered in this sec-
tion are therefore ranked according to the potential
turbulence and sediment resuspension at the sites. The
considerations are similar to those used in ranking the
disposal options in Case Study I, and a detailed geochemical
justification of this strategy may be found in Appendix L to
that section. Artificially created land areas, which are
subaerially exposed, present quite different geochemical
conditions and are discussed in detail in this section.
(1) Metals
Using the criteria developed previously for assessing
the potential release of contaminants in which we considered
the degree of sediment resuspension as the determining
factor, the undiked overboard option has the greatest poten-
tial of the submarine sites considered here for release of
metals. Diking of subaqueous sites and keeping the dredged
material below the water surface, would significantly reduce
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sediment resuspension and the potential for release of metals.
Disposal at the two other submarine sites—Kent Island and
the deep trough—would also probably effectively retain metals
within the disposal pile because of their relatively quiescent
conditions.
The construction of new fastland or wetland using dredged
materials and the consequent exposure of these materials to
the atmosphere permits large masses of sediment to be oxygen-
.ated (Mang et al.; 1978). One result of this oxygenation is
a reduction in the strength of the sediment-contaminant
association with a corresponding increase in the availability
of contaminants to solution. The subaerial exposure of land
created from dredged materials provides opportunities for
mobilization and movement of contaminants by percolating
rainwater. The freshwaters, which are highly oxygenated, will
eventually satiate the large oxygen demand of the sediment
pile and begin to dissolve the once insoluble reduced metals
compounds. These might then work their way into streams and
the nearby Bay, and be available for direct uptake by organ-
isms. They might also penetrate into groundwaters causing
contamination of drinking waters.
Detailed monitoring performed at the Pearce Creek
onshore disposal site in November 1976 (Harmon, 1976) revealed
considerable water quality degradation. The effects on the
main body of the Chesapeake Bay from this operation are
unknown because no monitoring was performed in adjacent open
waters. Pearce Creek itself, which discharges to the open
Bay through sluices, showed significant levels of dissolved
heavy metals, and smaller, but measurable decreases in dis-
solved oxygen. The pH of the Creek was significantly reduced.
The biota were apparently stressed as evidenced by substan-
tially reduced benthic community diversity indices. The
possibility exists that these impacts are caused by the con-
fined disposal area which provides limited dilution potential
for contaminants. Significant concentrations of dissolved met-
als such as those reported for Pearce Creek, have never been
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observed at open water locations where dilution is rapid and
effective.
We consider that the release of metals from onshore dis-
posal sites is likely because the metals have the potential
to be soluble and to come in contact with migrating solutions.
Oxygenated rain water provides the dissolution mechanism and
a vector for the dissolved products.
(2) Nutrients
The expected rate of expulsion of nutrients from a sub-
marine disposal pile with a volume of0.75xlO m (Ix
6 -5
10 yds ) of material has been calculated and compared with
natural nutrient regeneration rates in Appendix L, part 2.
The conclusion reached that the amount of nutrients released
from the compacting pile was small compared with the amount
of natural nutrient regeneration is valid for the submarine
sites under consideration in this section as well.
The amount of nutrients released through disposal in
fringing areas is likely to be larger for two reasons. First,
the amount of compaction is larger than for submerged sedi-
ment piles and therefore more pore waters are expelled.
Second, subaerial exposure of the disposal area allows rain
water to replace and "flush out" pore waters from the pile,
enhancing the flux of nutrients. It is still unlikely,
however, that the amount of nutrients released from such a
pile over an extended period, if given ample opportunity for
dilution, would cause significant increases in nutrient
concentrations in adjacent open waters. This may not be the
case for small semi-enclosed water bodies, such as tidal
creeks that receive the effluent from large deposits of
dredged materials.
(3) Chlorinated Hydrocarbons
At the present time predictions of the long-term geo-
chemical behavior of chlorinated hydrocarbons cannot be
made with the same degree of confidence as predictions for
metals (see Appendix L). A conservative approach requires
that we assume that the distribution coefficient of CHCs
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between the solid and dissolved phases in sediment-water
systems is measurably large (as opposed to metals, for exam-
ple) , and that this results in the molecular diffusion of
CHCs across the sediment-water interface to the near-bottom
waters. The environmentally conservative disposal strategy
is to minimize this flux. Disturbance of the sediment pile
by physical processes and by bioturbation increases the rate
of diffusion and should be minimized.
Although the release of chlorinated hydrocarbons from
dredged materials is possible for all the disposal strategies
we considered, theoretically the rate of release is likely
to be greatest in those environments where the sediments are
disturbed most frequently. Using this criterion, the possible
rate of release of CHCs from dredged material disposed at the
various submarine locations considered here can be ranked
from slowest to fastest as: diked and submerged, deep trough,
Kent Island dump site, and undiked overboard. The greater
amount of compaction and subaerial exposure of material
disposed in fringing areas may enhance the rate of CHC
release over that at submarine locations.
References
Harmon, G.H. 1976. Report on the impact of the Chesapeake
and Delaware Canal dredged spoil disposal operation of
November 1976 on the water quality at the Pearce Creek
Disposal site. Maryland Water Resources Administration.
13pp (also unpublished data).
Mang, J.L., J.S. Lu, R.J. Lofy, R.P. Stearns. 1978. A
study of leachate from dredged material in upland areas
and/or in productive uses, DMRP Tech. Rept. D-78-20,
U.S.A.C.E., Vicksburg, Miss.
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APPENDIX DD
Oxygen depletion of ^ater column subsequent to
disposal of materials dredged from Baltimore Harbor
Approach Channels at proposed disposal sites (Table 8c).
As discussed in detail in Appendix M, it is unlikely
that the oxygen demand exerted by the submarine disposal
piles on the overlying waters will result in detectable
decreases in the dissolved oxygen content of near-bottom
waters. A similar argument can be made for disposal in
fringing areas.
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APPENDIX EE
Movement of material dredged from Baltimore
Harbor Approach Channels subsequent to
disposal at proposed sites (Table Bo).
Movement of dredged materials subsequent to disposal
results primarily by sediment resuspension by waves and tides
and fluid mud flow (Appendix N). Of the alternatives con-
sidered, diked areas and stabilized fringing areas are least
susceptible to sediment movement and shallow, unconfined open
water sites most susceptible. Movement of dredged materials
from the trough south of the Bay bridge and from the Kent
Island Site has been discussed in Appendix N. Movement of
sediment in the trough is considered to be less likely than
at the Kent Island site because of the trough's greater
depth and its steep sides.
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APPENDIX FF
Effect of changes in bottom topography at
Baltimore Approaches alternatives (Table 3a).
Possible effects of changes in bottom topography as a
result of dredging and spoil operations would include changes
in the distribution and strength of the currents; changes in
the intensity of turbulence; and changes in the usability
of the area for fishing and boating.
Disposal of spoil overboard in areas adjacent to the
Baltimore Harbor approach channels would have negligible
effect on the distribution of currents in the cross-section
and on the intensity of turbulence. Since the material
being dredged from these channels is for the most part silt
and clay, the spoil will, soon after disposal, be spread by
the effects of gravity and by the currents over a wide area.
Much of it in fact ultimately will return to the channel.
Any temporary decrease in depth over the adjacent area will
be small, and will be offset by the increase in depth of
the channel as a result of dredging. Thus, the average
current speed in any given cross-section would not be changed
by the dredging and spoiling operation, and any change in
the distribution of currents in the section would be
negligible.
Subsequent to disposal of the spoil, there would not be
any significant effects of overboard disposal in areas
adjacent to the channel on the use of such areas for fishing
and boating. Note that we are here discussing any physical
effects , such as interference with fishing gear or creation
of hazards to navigation (i.e., shoal areas), and not to any
strictly biological effects on fishing success.
The creation of confined, submerged disposal areas
adjacent to the Baltimore Harbor Approach Channels could
possibly have some effects on the distribution of currents
in the reach of the Bay containing such a disposal area,
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and also on the use of such areas for fishing and boating.
The degree of impact of a confined, submerged disposal area
will depend on specific features of location and size. In
order to examine possible effects of such disposal areas,
we have considered two plausible cases with respect to
location and dimensions of the confinement structures.
We have first considered the possible effects of
locating a confined, submerged disposal area in the existing
designated spoil area that runs parallel to the Brewerton
Channel Eastern Extension, and lies to the north of this
channel. Depths in this area range from about 15 feet
(4.6 meters) to about 18 feet (5.5 meters) below mean low
water. A rectangular diked containment area, 8000 feet
long (in the direction parallel to the Brewerton Channel
Eastern Extension) and 7000 feet wide could hold 2.07 mil-
lion cubic yards per foot of fill. (5.21 million cubic
meters per meter of fill). Constructing the dikes to
extend from the bottom with an average depth of 16 feet
(4.9 meters), to within 3 feet (2.4 meters) of the surface
would provide confined, submerged disposal for 16.6 million
cubic yards (1.2.7 million cubic meters) of spoil.
Such a disposal area would extend along the bottom for
16% of the width of the cross-section that extends from
North Point to Swan Point. It would, however, reduce the
area of this cross-section by only 9.7%. Tidal elevations
upstream from this section would not be measurably affected
by such a structure. Peak ebb and flood current speeds in
this cross-section would increase, on the average, by about
10%, with somewhat larger increases near the submerged
structure. The maximum ebb and flood current speed through
this section is about 1.2 ft sec (37 cm sec ), and a 10%
increase would not result in current speeds exceeding those
naturally found at sections both north and south of this
cross-section.
This area cannot be used for fishing with deep drift
nets since there are natural shoals which run laterally
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across the Bay, with minimum depths of only 4 feet, just to
the north, and Sevenfoot Knoll and Sixfoot Knoll lie to the
south of the Brewerton Channel Eastern Extension. Construc-
tion of such a submerged confinement area would limit, to
some extent, navigation of vessels with drafts greater than
eight feet through the area. However, the above-mentioned
shoals already limit navigation outside the established
channel areas for such craft.
We also considered a confined, submerged disposal area
running parallel to and to the east of the Craighill Channel,
A rectangular diked area 3000 feet (915 m) wide and 18,000
feet (5490 m) long (in a direction parallel to the channel)
could hold 2.0 million cubic yards per foot of fill (5.02
million cubic meters per meter of fill). The bottom
depths in this reach average about 15 feet (4.6m). If the
confining dikes were built to within 8 feet (2.4 m) of the
surface, such a disposal area could contain 14.0 million
cubic yards (10.7 million cubic meters) of spoil.
Such a disposal area would occupy about 6.9% of the
width of the bottom of the cross-section between Bodkin
Point and Swan Point. Construction of such a containment
facility to within 8 feet of the surface would reduce the
area of this cross-section by about 3.0%. The peak tidal
currents would, on the average, be increased by about this
same amount (3.1%). Such an increase would not result in
current speeds exceeding those found in sections in the
Bay both north and south of this section.
Because of Sixfoot Knoll and Sevenfoot Knoll, naviga-
tion of vessels having drafts greater than the 8 foot depth
of the example containment area is already severely
restricted. For this same reason, fishing using drift nets
is not practical in this region.
The construction of such submerged dikes could be a
local benefit to sports fishermen. Such dikes could serve
to provide hard substrate for sessile organisms, and a
consequent attraction for forage fish and game fish.
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The use of the Kent Island Dump Site to continue to
receive spoil from the dredging of the Baltimore Harbor
Approach Channels would result in small increases in the
maximum speed of the tidal currents in that area of the
Chesapeake Bay. The active area of dump site extends from
just north of the Bay Bridge to just south of Love Point.
The area of this dump site is some 50 million square ft
(4.65 million square meters). Each foot of fill over this
area represents 1.85 million cubic yards (4.64 million cubic
meters per meter of fill). Five feet more of spoil disposed
of over the area of the Kent Island Dump Site would repre-
sent 9.25 million cubic yards (7.1 million cubic meters) of
dredged material.
The Kent Island Dump Site as now laid out occupies
about 18% of the bottom width of the cross-section extending
from Sandy Point to Kent Island, along a line perpendicular
to the axis of the Bay. Five feet of additional fill over
the area of the dump site would result in a decrease in the
present cross-sectional area by some 2.8%. There would then
be a 2.9% increase in the maximum ebb and flood currents in
the cross-section. This small increase would not signifi-
cantly increase scour nor adversely affect navigation.
Deep draft vessels traverse the designated channel to the
west of the dump site and hence the decrease in depth over
the spoil area would not have any significant effect on
waterborne transport through the area.
The deep trough south of the Bay Bridge has a width
between the 60 ft (18.3 m) depth contours of from 3800 ft
(1160 m) to over 6000 ft (.1830 m) with an average of 4620 ft
(1400 m). For each nautical mile (6080 ft or 1854 meters)
of length of this trough, one foot of fill at and below the
60 ft (18.3 m) contour would represent 1.04 million cubic
yards (2.61 million cubic meters per meter of fill). Five
ft (1.5 meters) of fill distributed over a disposal area
in the trough contained within the 60 foot (18.3 meter)
contours and extending over a length of five nautical miles
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(9270 meters), or over several segments aggregating to
5 nautical miles, would then provide for the disposal of
about 26 million cubic yards (19.9 million cubic meters)
of spoil.
Such a 5 foot (1.5 m) fill between the 60 ft (18.3 m)
depth contours in the deep trough would represent about 2%
of the cross-sectional area for the typical cross-section
south of the Bay Bridge. The corresponding 2% increase in
maximum ebb and flood current speeds averaged over the
cross-section where such fill took place would not cause
any significant effect on scour or on navigation.
The disposal option which used spoil to create marsh-
land from protected shallow water areas adjacent to the
upper Bay would obviously change the local circulation,
providing, in fact, an entirely new hydrodynamic regime as
well as an entirely new biological habitat. The effects
that the creation of wetlands by spoil disposal in protected
shallow water areas adjacent to or along the shores of the
upper Chesapeake Bay would have on currents in adjacent
open waters would depend on the fraction of the cross-section
of the Bay represented by such fill operations. In general,
the effects of this option of spoil disposal would be
negligible on the distribution of currents in the waters of
the adjacent open Bay.
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APPENDIX GG
Time for recovery of benthic communities at
disposal sites considered for ria.teria.ls dredged
from Baltimore Harbor Approach Channels (Table 3d).
1. Biomass
Numerous studies (see Appendix P) have described the
rapid repopulation of the bottom by infaunal organisms in
areas following dredged material disposal. In the absence
of detailed ecological information for the specific disposal
sites we considered, there is no reason to expect that
recovery of biomass would be less rapid at these sites than
at other sites which have been studied. Any benthos exist-
ing at a site that is built-up to above the water surface
will of course be permanently destroyed (VIMS, 1977).
2. Diversity
The entries in Table 8d regarding the time required for
recovery of benthic diversity at the various disposal sites
reflect the arguments presented in Appendix P. Briefly
summarized, communities naturally exposed to large environ-
mental variability have a low diversity and will be quick to
recover to pre-disposal conditions. More mature communities,
characteristic of more stable environments, take longer to
recover to pre-disposal diversity levels.
Lack of detailed information on the structure of the
benthic communities at the Kent Island disposal site and at
the overboard sites near the Baltimore Harbor Approach
Channels precludes documentation of the times required for
recovery of diversity by the inbenthic communities. It seems
likely that the low summer dissolved oxygen levels of bottom
waters at the Kent Island and trough sites cause significant
seasonal mortality of benthic organisms. These communities
must be re-established by recruitment of juveniles each year
to maintain even tenuous populations in these areas. It
appears very unlikely that disposal of dredged materials
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would reduce significantly the already low diversity that
must characterize these areas, particularly in the trough.
VIMS. 1977. Habitat development field investigations,
Windmill Point Marsh Development Site, James River, Va.,
D.M.A.P. Tech. Kept. D-77-23, U.S.A.C.E., Vicksburg, Miss,
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APPENDIX HH
Uptake of eonta.mi.na.nts by organisms at
alternative disposal sites for materials dredged
from the Baltimore Harbor Approach Channels ('I'able 3d).
A. Metals
1. Benthos. The mechanisms of trace metal uptake
by infaunal and epifaunal benthic organisms have been dis-
cussed in Appendix G, part la. Uptake of metals by benthos
does occur, but we have only limited knowledge of its
effects. The possibility exists that metals in material
dredged from this project are in forms that are readily
available to organisms, but experimental confirmation of
this is lacking. The best disposal site selection criterion
appears to be "like-on-like." This criterion calls for
selection of a site where ambient metals concentrations are
comparable to those in the materials to be dredged. As
discussed in the introduction, disposal of materials dredged
from the Baltimore Approach Channels at the sites proposed
in this section would not result in significant elevation of
contaminant concentrations in sediments at those sites.
This is not to suggest that trace metal uptake by benthic
organisms will not occur, only that it will not be accelerated
by disposal. At present, there is no way of evaluating the
relative possibilities of uptake at the various disposal site
options.
2. Plankton. Uptake of metals by plankton occurs
mostly from the soluble form (Bryan, 1971) and therefore
will be increased only in those disposal areas where signi-
ficant dissolved metals are released. Examination of
Table 8c shows that release of dissolved metals is likely to
occur only in fringing wetland sites. Therefore, uptake of
metals from dredged materials by plankton may possibly occur
in the open waters adjacent to such sites.
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3. Nekton. Uptake of metals by fish occurs from
the dissolved state and also from metals incorporated into
plankton and benthos. Disposal sites which neither release
dissolved metals nor impact benthos will not lead to uptake
of metals by nekton.
4. Emergent grasses. Several studies (Lee et al.,
1978; Gambrell et al., 1977; Center for Wetland Resources,
1977) have described the ability of marsh grasses to take-up
significant quantitite os heavy metals from fine-grained
sediment. Because salt marsh detritus may be exported from
marshes to surrounding open waters, this provides a mechanism
for the dispersal of toxic metals over a larger area and for
their entry into numerous organisms. Only fringing area
disposal sites are subject, of course, to emergent grass
uptake of metals.
B. CHCs
Because long term desorption of chlorinated hydrocarbons
from submarine disposal piles can not be ruled out (see appen-
dices L, v), and because these substances are known to be
taken up from solution by plankton, mollusks (Duke et al.,
1970), and nekton (Smith and Cole, 1970), uptake of CHCs by
these organisms is probable. It is unlikely, but not impos-
sible, that significant quantities of CHCs desorbed from
submarine sites would impact fringing areas. If fringing
areas are constructed from CHC contaminated materials, uptake
by marsh plants is possible.
References
Bryan, G.W. 1971. The effect of heavy metals (other than
mercury) on marine and estuarine organisms. Proceedings
Royal Society of London. B177:389-410.
Center for Wetland Resources, Louisiana State Univ. 1977.
Trace and Toxic Metal Uptake by Marsh Plants as Affected
by Eh, PH and Salinity. D.M.R.P. Tech. Rept. D-77-40
U.S.A.C.E., Vicksburg, Miss.
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Duke, T.W., J.I. Lowe, and A.J. Wilson, Jr. 1970. A poly-
chlorinated biphenyl (Arochlor 1254) in water sediment,
and biota of Escambia Bay, Fl. Bull, of Environmental
Contamination and Toxicology. 5:171-180.
Gambrell, R.P., V.R. Collard, C.N. Reddy, and W.H. Patrick,
Jr. 1977. Trace and toxic metal uptake by marsh plants
as affected by Eh, pH, and salinity. Tech. Rept. D-78-6,
U.S. Army Engineer Waterways Experiment Station, Vicksburg,
Miss.
Smith, R.M. and C.F. Cole. 1970. Chlorinated hydrocarbon
insecticide residues in winter flounder, Pseudopleuroneetas
ameri-eanus, from the Weweantic River Estuary, Ma. J. of
Fisheries Res. Bd. of Canada. 27:2734-2380.
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APPENDIX II
i
Effects of different disposal strategies on the
frequency of dredging required to maintain
Baltimore Harbor Channels (Table 11).
If dredged materials are not sufficiently removed or
isolated from the dredging site, waves and tides may cause
the return of these materials to the channel. Inasmuch as
most previous disposal of Baltimore Harbor materials has
been at the Kent Island site or on fringing areas (Md. Dept.
of Natural Resources, 1976), continued use of this and
other geographically removed locations will not result in
any change in the historical frequency of dredging required
to maintain the Harbor channels at their present project
depth. Use of uncontained, overboard sites close to the
channels might increase the frequency of dredging required
for channel maintenance because of increased return of
dredged materials to the channel.
Reference
Hamons, F., ed. 1976. Monitoring of open water dredge
material disposal operations at Kent Island disposal site
and survey of associated environmental impacts. Maryland
Dept. of Natural Resources Final Rept., 310pp.
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APPENDIX JJ
Assessment of the degree of turbulence at
the proposed disposal sites for materials
dredged from Baltimore Harbor Channels (Table 11).
Unconfined overboard disposal sites are the more turbu-
lent of the two submarine options we considered for disposal
of materials dredged from the Baltimore Harbor Channels.
The confined, submerged, overboard option is less turbulent.
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APPENDIX KK
Amount of sediment resuspension at the proposed
disposal sites for materials dredged from
Baltimore Harbor Channels (Table 11).
For a discussion of the factors controlling bottom
sediment resuspension see Appendix B. Without detailed
information on the physical and biological characteristics
of sediment at the proposed disposal sites, we must rank
the sites in terms of the degree of bottom water turbulence.
There are two submarine disposal options under consideration
to receive Baltimore Harbor channels material. The confined
overboard site will be subject to substantially less sedi-
ment resuspension than the unconfined, overboard disposal
option.
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APPENDIX LL
Excess turbidity in the water column during
disposal operations for materials dredged from
Baltimore Harbor Channels (Table 12a).
The possibility of generation of excess turbidity by
the disposal methods under consideration has been discussed
in detail in Appendix D. The conclusion, that any excess
turbidity generated during disposal will be temporary and
local in extent, holds for the disposal options considered
for materials dredged from Baltimore Harbor Channels.
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APPENDIX MM
Assessment of contaminant releases to the water column
during disposal operations of materials dredged from
Baltimore Harbor Channels (Table 12a).
See Appendix E for a detailed discussion of the geo-
chemical processes that control the possible release of
metals, nutrients, and CHCs from dredged materials during
disposal operations.
(1) Metals
The conclusion reached in Appendix E, that release of
metals from dredged materials during disposal operations
is unlikely, holds for the disposal methods and locations
we considered for materials dredged from Baltimore Harbor
Channels.
(2) Nutrients
The conclusion reached in Appendix E, that releases of
nutrients from the dredged material during disposal will
have a negligible impact on the water column, is equally
applicable to all the dredging/disposal options considered
for materials dredged from Baltimore Harbor Channels.
(3) CHCs
The difficulties involved in predicting the environ-
mental behavior of CHCs have been described in detail in
Appendix E, Release of CHCs from Baltimore Harbor Channels
material during disposal operations may be more likely than
from sediments considered in the other case studies in this
report for two reasons. First, the Baltimore Harbor mate-
rials are much higher in CHC content (see Table 10). If, as
has been assumed, there is a measurable distribution
coefficient for CHCs between the solid and dissolved states,
a higher CHC concentration in the adsorbed state produces a
higher concentration in the water. Second, Baltimore Harbor
materials contain significant levels of hexane extractable
compounds (see Table 10). Since CHCs are fat soluble, these
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may increase the solubility of sediment-associated CHCs.
Both of these effects remain unevaluated. Until experi-
mental evidence indicates otherwise, we should consider that
significant release of CHCs from Baltimore Harbor Materials
during disposal operations is a distinct possibility.
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APPENDIX NN
Oxygen depletion of the water column during
disposal of materials dredged from
Baltimore Harbor Channels (Table 12a).
In Appendix F we considered the possible oxygen deple-
tion of the water column during disposal operations. The
conclusion reached there, that any reduction is temporary
and local in extent, holds for the disposal options consid-
ered for materials dredged from the Baltimore Harbor channels
as well.
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APPENDIX 00
Zoological affects of increased water column
turbidity during disposal of Baltimore
Harbor Channels material (Table 12b).
1. Phytoplankton
Reductions in incident illumination and the consequent
possible decrease in phytoplankton photosynthetic activity
as the result of increased water column turbidity are con-
fined to the temporal and spatial limits of the turbidity
plume. Because this plume is transitory and local (see
Appendix D) in extent, associated decreases in phytoplankton
photosynthesis are also temporary and local. It is highly
unlikely that the small area affected by the increased tur-
bidity caused by disposal operations can have more than a
negligible effect on the total estuarine phytoplankton
primary production (Flemer, 1970).
2. Zooplankton
The temporary and local nature of the turbidity plume
associated with dredged material disposal (see Appendix D)
limits any effect upon zooplankton to a small area.
Estuarine zooplankton must already be adapted to coping with
levels of suspended sediment similar to those found over
much of the excess turbidity plume from dredged material
disposal (Goodwyn, 1970).
3. Nekton
The generally small area that is temporarily affected
by excess turbidity during dredged material disposal can
have no more than a negligible effect on nekton populations
in the estuary (Dovel, 1970) .
4. Benthos
The generally small area that is temporarily affected
by excess turbidity during dredged material disposal can
have no more than a negligible impact on benthic populations
outside of the immediate disposal area (Pfitzenmeyer, 1970).
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5. Fish Eggs and Larvae
Numerous studies (Schubel and Wang; 1973, Shark et al.;
1970, Auld and Schubel; 1978) have indicated that the survival
of eggs and larvae of typical estuarine fishes (yellow perch,
blueback herring, alewife, American shad, white perch, striped
bass) are not significantly decreased by exposure to suspen-
sions of natural fine-grained relatively uncontaminated
sediments with concentrations much greater than those typi-
cally observed, even during dredging and disposal. Based on
these studies we conclude that the excess concentrations of
suspended sediment that result from dredging and disposal of
relatively uncontaminated sediments do not represent a
significant hazard to fish eggs and larvae as far as acute
effects are concerned. Chronic effects have, however, not
been adequately investigated.
References
Auld, H.H. and J.R. Schubel. 1978. Effects of suspended
sediment on fish eggs and larvae: a laboratory assessment.
Est. Coast. Mar. Sci. 6:153-164.
Flemer, D.A. 1970. Project B, Phytoplankton. Pages 16-25
in Gross physical and biological effects of overboard
spoil disposal in upper Chesapeake Bay. Natural Resources
Inst., Special Rept. #3, Ches. Biol. Lab., Univ. of Md.
Goodwyn, F. 1970. Project D. Zooplankton. Pages 39-41 in
Gross physical and biological effects of overboard spoil
disposal in upper Chesapeake Bay. Natural Resources Inst.,
Special Rept. 13, Ches. Biol. Lab., Univ. of Md.
Pfitzenmeyer, H.T. 1970. Porject C, Benthos. . Pages 26-38
in Gross physical and biological effects of overboard
spoil disposal in upper Chesapeake Bay. Natural Resources
Inst., Special Rept. #3, Ches. Biol. Lab., Univ. of Md.
Richie, D.E. 1970. Project F, Fish. Pages 50-63 in Gross
physical and biological effects of overboard spoil disposal
in upper Chesapeake Bay. Natural Resources Inst., Special
Rept. #3, Ches. Biol. Lab., Univ. of Md.
185
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Schubel, J.R. and J.C.S. Want. 1973. The effects of sus-
pended sediment on the hatching success of ?e?ca
flcLveseens (yellow perch) , Mcrone am&z"ieana (white perch) ,
Mopone saxat-ilis (striped bass) and Alosa pseudoharengus
(alewife) eggs. Special Report No. 30, Ches. Bay. Inst.,
Johns Hopkins Univ., Ref. 73-53, 77pp.
Sherk, J.A. and L.E. Cronin. 1970. The effects of suspended
and deposited sediments on estuarine organisms. An anno-
tated bibliography of selected references, Univ. of Md. ,.
National Res. Inst., Ref. 70-19, 61pp + addendum.
186
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APPENDIX PP
Smothering of benthos by disposal of Balt
Harbor materials -in various disposal sites (Table 12b).
At the submarine disposal sites considered in this sec-
tion smothering of benthos by disposal of dredged material
will probably be complete. Recolonization will occur rela-
tively rapidly, however, in unconfined (overboard) sites
(See Appendix XX). Recovery in confined submarine sites
will be slower and complete recovery may not occur. With
wetland and island construction, the pre-disposal communities
will be permanently altered.
187
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APPENDIX QQ
Exclusion/attraction of fish at Baltimore
Harbor Alternatives (Table 12b).
During disposal operations attraction of local finfish
to the turbidity plume has been occasionally observed. This
attraction has been attributed to releases of particulate
organic matter associated with the dredged material which
serve as a food source for the fish. Finfish have also been
observed to be repelled by the turbidity plume, perhaps in
response to the generally lowered dissolved oxygen levels in
its immediate vicinity. Generally it has been observed that
fish are more sensitive to oxygen depletion than to excess
turbidity, and appear to be repelled from the disposal area
before encountering the high turbidity levels located within
the plume. Because of this defensive mechanism, and also
because of the limited area strongly affected by increased
turbidity during disposal (see Appendix D), disposal opera-
tions do not pose a threat to resident finfish populations
at locations where sufficient space is available to enable
fish to avoid the plume. This is true for all the locations
under consideration in this report.
188
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APPENDIX RR
Uptake of contaminants by biota during the
disposal of Baltimore Harbor Channels material
at various submarine disposal sites (Table 12b).
1. Metals
Because the release of soluble metals during disposal
is considered unlikely, benthos, plankton, and nekton will
not be subject to metals concentrations higher than ambient
and the rate of uptake of metals will not be affected. See
Appendix V for more detail.
2. CHCs
Because the release of soluble CHCs during disposal
operations is considered possible, benthos, nekton, and
plankton might take up these compounds at faster rates and
in greater amounts as the result of disposal (see Appendix
E). Evaluation of the magnitude of this uptake is impos-
sible without knowledge of the CHC distribution coefficient,
We recommend that this be determined particularly for
Baltimore Harbor materials, some of which are highly con-
taminated with CHCs.
189
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APPENDIX SS
Excess turbidity in water* column subsequent
to disposal of ma.-tSTia.ls dredged from
Baltimore Harbor Channels (Table 12a).
The conclusion reached in Appendix K that excess
turbidity subsequent to disposal operations would be negli-
gible is true for all the sites under consideration here
except the undiked overboard site within Baltimore Harbor.
The possibility exists that, because the Harbor is not
normally subject to extreme changes in turbidity, possible
sediment resuspension from the undiked site (see Appendix
KK), might create a persistent source of excess turbidity.
The effects, however, would be local and small.
190
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APPENDIX TT
Increased contaminant releases to water
column subsequent to disposal of
Baltimore Harbor dredged materials.
1. Metals
Although contaminated with metals to a greater degree
than material dredged from either of the other Projects, the
geochemical mechanisms binding the metals to these sediments
are expected to be similar. Because of this, the conclusions
expressed in Appendix E, that with subaqueous disposal
releases of metals to solution will be minor, hold true here
as well. A confined submerged disposal site is considered
best because it minimizes sediment resuspension and oxidation
of reduced metal compounds.
The subaerially exposed disposal alternatives, island or
marsh creation, and upland disposal, all are considered more
likely to result in increased metal releases to solution
(Hang et al., 1978). This is because of the increased
probability that the reduced sediments will be oxidized.
Although no studies have been published on the chemical
composition of runoff and groundv/ater flow from dredged mate-
rial islands, and the possibility exists that the most highly
contaminated materials could be isolated through appropriate
engineering structures such as the use of "nested dikes," the
critical studies have not, in our opinion, been conducted to
demonstrate that contaminants would not be released in solu-
tion with subaerial disposal.
2. Nutrients
Releases of nutrients from the submerged disposal options
considered for Baltimore Harbor materials are expected to be
small in relation to the amount of nutrients naturally
regenerated from Bay sediments, the calculations leading to
this conclusion are detailed in Appendix E-2.
This is not true for the subaerially exposed alternatives
191
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Here percolating groundwater solutions have a high potential
for releasing large quantities of 11 and P compounds (Mang
et al.; 1978).
3. CHCs
As discussed in Appendix E-3, the release of CHC com-
pounds from dredged materials is considered possible. There
is a somewhat larger probability of such release occurring
from subaerially exposed disposal alternatives because of the
possible role of percolating groundwater solutions as a
vector.
Reference
Mang, J.L., C.S. Lu, R.J. Lofy, R.P. Stearns. 1978. A study
of leachate from dredged material in upland areas and/or
in productive uses. DMRP Tech. Rept. D-78-20, U.S.A.C.E.,
Vicksburg, Miss.
192
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APPENDIX UU
Oxygen depletion of the water column
subsequent to disposal of materials dredged
from Baltimore Harbor (Table 12c).
This has been considered in detail in Appendix M. The
conclusion that oxygen depletion would be undetectable under
the turbulent conditions encountered at the disposal sites
is unchanged for the disposal options considered for mate-
rials dredged from Baltimore Harbor Channels.
193
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APPENDIX W
Movement of materials dredged from
Baltimore Harbor Channels and placed at
various disposal sites (Table 12s).
As discussed previously in Appendix M, movement of
dredged materials subsequent to disposal is by sediment
resuspension and "fluid mud" flow along the bottom. Of the
two submarine disposal options considered for materials
dredged from Baltimore Harbor—confined and unconfined
overboard disposal—significant sediment movement can occur
only from the undiked option. The principal advantage of
enclosing the site is to reduce post-disposal movement of
sediment.
Movement of sediment from land sites by subaerial
erosion processes can be minimized if proper sediment con-
trol measures are taken.
194
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APPENDIX WW
Effect of changes of bottom topography at
Baltimore Harbor Alternatives (Table 12c).
Possible effects of changes in bottom topography as a
result of dredging and spoil operations would include
changes in the distribution and strength of the currents;
changes in the intensity of turbulence; and changes in the
usability for the area for fishing and boating.
Disposal of spoil overboard in areas adjacent to the
Baltimore Harbor channel would have negligible effect on
the distribution of currents in the cross-section and on
the intensity of turbulence. Since the material being
dredged from these channels is for the most part silt and
clay, the spoil will, soon after disposal, be spread by the
effects of gravity and by the currents over a wide area.
Much of it, in fact, ultimately will return to the channel.
Any temporary decrease in depth over the adjacent area will
be small, and will be offset by the increase in depth of
the channel as a result of dredging. Thus the average
current speed in any given cross-section would not be changed
by the dredging and spoiling operation, and any change in
the distribution of currents in the section would be
negligible.
Subsequent to disposal of the spoil, there would not
be any significant effects of overboard disposal in areas
adjacent to the channel on the use of such areas for fishing
and boating. Note that we are here discussing any physical
effects such as interference with fishing gear or creation
of hazards to navigation (i.e., shoal areas), and not to
any strictly biological effects on fishing success.
The creation of confined, submerged disposal areas
adjacent to the Baltimore Harbor Channel could influence the
distribution of currents in the reach of the Harbor contain-
ing such a disposal area, and also on the use of such areas
195
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for fishing and boating. The degree of impact of a confined,
submerged disposal area will depend on specific features of
location and size. There is very little space in Baltimore
Harbor inside of Hawkins Point (Francis Scott Key Bridge)
for confined, submerged disposal areas. The cost of dike
construction per cubic yard of capacity of the disposal area
decreases with increasing area inside the dikes. Thus from
considerations of cost effectiveness, it is doubtful that
confined, submerged disposal areas would be justifiable in
the inner half of the harbor. The only area in the Harbor
that appears suitable for such use is the reach just south
of the Brewerton Channel, and extending from the inner end
of Sparrows Point out to the mouth of the Harbor at the
Rock Point shoal/North Point section. In order to examine
the possible effects of a confined, submerged disposal area
adjacent to the Baltimore Harbor Channel we have considered
one plausible case of such a disposal facility located in
this outer Harbor area.
The case we considered assumes that a confined, sub-
merged disposal facility is established in the currently
discontinued spoil area south of the Brewerton Channel. A
rectangular shaped diked area, 4000 ft (1220 m) wide and
12,000 ft(3,660 m) long (in the direction parallel to the
Brewerton Channel) in the area just south-southwest of the
Channel, extending from the mouth of the Harbor (the Bodkin
Point to North Point transect) inwards to about opposite
the western end of Sparrows Point, is considered. The
depths in the region of this assumed facility average about
15 ft (4.6 m). If the dikes were built upwards from the
bottom to within seven ft (2.1 m)'of the surface, this
facility could hold 14.22 million yards (10.88 million m ).
This facility would occupy 28.5% of the width of the
bottom of the Bodkin Point to North Point transect. Filled
to within 7 ft (2.1 m) of the surface, this diked facility
would result in a decrease in the cross-sectional area by
15.3% and a consequent increase in the sectionally averaged
196
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peak ebb and flood velocities by 18%. The tidal current
velocities are, however, quite small within the Harbor,
and even at the transect at the mouth, the maximum ebb and
— 1 ^
flood velocities are only about 0.34 ft sec (10.3 cm sec"1}
Increasing these values by 18% would not result in any
significant increase in scouring or hazard to navigation.
The construction of such a submerged diked facility
would result in restrictions for transit of vessels having
drafts of between 7 ft (.2.1 m) and 15 feet (4.6 m) . The
dikes of this disposal area could be located so that such
craft having as a destination Rock Creek or Stony Creek
could pass southward of the facility.
The construction of a diked island inside or outside
of the Harbor for confinement of dredging spoil would have
effects on circulation similar to those described for the
submerged diked areas. To illustrate the possible effects
of such a facility, we have considered the case of the
proposed Hart and Miller Islands disposal area.
This facility as currently planned will be a rectangu-
lar diked enclosure extending out from Hart Island and
Miller Island. These islands would form the bulk of the
west-northwest boundary of the enclosure. The critical
cross-section of the Bay with respect to this structure runs
from Miller Island in a east-southeast direction to the
eastern shore just south of Tolchester Beach. The width of
this section would be reduced by about 14.3% by construction
of the diked enclosure at Hart and Miller Islands. The area
of this cross-section would be reduced by 7.2%, and conse-
quently the peak ebb and flood tidal velocities would be
increased by 7.8%. The resulting maximum tidal velocities
would average about 0.8 ft/sec (24 cm sec ) over the cross-
section. Velocities of this magnitude are found at sections
of the Bay both north and south of this transect. No signi-
ficant increase in scour or hazard to navigation would
occur as a result of this increase in velocity.
Turbulence would be somewhat increased in the vicinity
197
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of the dikes forming the enclosure. The outside of the
dikes might also prove to be a desired substrate for sessile
organisms. These two facts could make the area of the Bay
adjacent to the site attractive to forage fish, and hence to
game fish. This possible benefit is at least somewhat off-
set by the loss of the area of the Bay covered by the
artificial island for pleasure boating. Note that there is
no commercial fishing or any significant commercial boat
traffic in this area.
The disposal option which uses spoil to create marsh-
land from protected shallow water areas adjacent to the
Harbor would obviously change the local circulation, pro-
viding in fact an entirely new hydrodynamic regime as well
as an entirely new biological habitat. The effect that the
creation of wetlands by spoil disposal in protected shallow
water areas adjacent to or along the shores of the Harbor
would have on currents in adjacent open waters would depend
on the fraction of the cross-section of the Harbor repre-
sented by such fill operations. In general, the effects of
this option of spoil disposal would be negligible on the
distribution of currents in the waters of the adjacent open
Harbor.
198
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APPENDIX XX
Time required for the recovery of the benthic
community subsequent to the disposal of material
dredged from Baltimore Harbor Channels (Table 12d).
A. Biomass
Although specific information on benthic community
recruitment is limited for Baltimore Harbor, data obtained
from similar environments (see Appendix P) indicate that
recovery of benthic biomass subsequent to disposal of
Baltimore Harbor Materials will be rapid; complete recovery
within 1.5 years. The benthos in the inner Harbor are
generally impoverished (Tsai et al., 1979) and are dominated
by worms. It is unlikely that the temporary destruction of
a small part of this biomass by disposal operations could
produce a significant and persistent ecological effect.
3. Diversity
Although specific information on the recovery of benthic
diversity following depopulation of Baltimore Harbor sedi-
ments is not available, similar areas (see Appendix P) have
recovered diversity within 1.5 years.
Reference
Tsai, C-F, J. Welch, K-Y Chang, J. Shaeffer and L.E. Cronin.
1979. Bioassay of Baltimore Harbor Sediments. Estuaries
2(3) -.141-153.
199
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APPENDIX YY
Uptake of contaminants by organisms subsequen
disposal of Baltimore Harbor Channel materials (Table 12d).
A. Metals
1. Benthos. The conclusion reached in Appendix Q,
that benthic organisms have the ability to take up metals
directly from sediment, remains unchanged for the Baltimore
Harbor materials. It is important, however, that the benthic
populations currently in the inner Harbor are impoverished,
and that therefore there are few organisms available for up-
take of metals if the dredged materials are disposed within
this area.
2. Plankton. Because the most important mechanism
of planktonic metals uptake is directly from solution (see
Appendix Q), only those disposal options that may release
soluble metals have the possibility to directly affect
plankton. Of the disposal options considered for material
dredged from Baltimore Harbor Channels, island construction,
fringing areas, and upland disposal, all are considered to
have the potential for release of soluble metals. Possible
planktonic uptake of metals is limited to open waters
adjacent to these disposal sites. Because release of
soluble metals from the submarine sites is considered
unlikely, disposal of Baltimore Harbor Materials in these
sites is considered unlikely to affect metals levels in
plankton.
3. Nekton. Fish also dominantly take up metals
from the dissolved state. Therefore only those sites where
soluble metals release is considered possible may impact
fish. These are the same disposal options that will directly
affect plankton and include upland disposal, island construc-
tion, and fringing areas.
4. Emergent Grasses. Emergent grasses—plants
growing in the intertidal zone—have the potential to take
200
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up metals from their substrate (see Appendix HH). Of the
disposal options considered here, only salt marsh creation,
and possibly island construction, would place dredged
materials in the intertidal zone. These are therefore the
only options where metals uptake by emergent grasses would
be possible.
5. Terrestrial Plants. Terrestrial plants have
the ability to take up metals from their soil. Of the dis-
posal options for Baltimore Harbor materials considered
here, new terrestrial land will be created only in island
creation and upland disposal. Terrestrial plants may
possibly uptake metals from dredged materials if these
options are used.
3. CHCs
1. Benthos. Benthic organisms have the ability to
take up CHCs from the sediments they inhabit (see Appendix
Q). Of the disposal options considered here to receive
Baltimore Harbor materials, only disposal sites alongside
the channel, confined or unconfined, are inhabited by benthic
organisms. Uptake of CHCs by faenthic organisms may occur if
these options are utilized. There is no reason to believe,
however, that the uptake of CHCs by benthos will be increased
necessarily if these disposal options are utilized. Organ-
isms inhabiting these areas are already exposed to sediment
CHC levels similar to those of the dredged material.
2. Plankton. Plankton are most likely to take up
CHCs directly from solution. All the disposal options con-
sidered here for Baltimore Harbor materials may lead to
release of CHCs in the soluble state. Therefore plankton
inhabiting waters near these proposed disposal options have
the potential for increased CHC uptake subsequent to dis-
posal operations. Increased uptake of CHCs by plankton is
much less- likely at the submerged inner Harbor sites, then
at the alternative sites considered. Because little is
known about the environmental chemistry of CHC compounds,
there is little reason to believe that the process of
201
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dredging and disposal increases CHC solubilization from
sediment. Plankton inhabiting the inner Harbor are already
exposed to high CHC levels which probably will be neither
reduced nor increased if dredged material disposal occurs
there.
3. Nekton. Fish dominantly take up CHCs from
solution. Therefore the previous discussion of the possible
planktonic uptake of CHCs applies also to nekton. Increased
uptake of CHCs by nekton is possible from utilization of all
the disposal options considered, but is less likely if the
along-channel submerged option is used.
4. Emergent Grasses. Emergent grasses—plants
growing in the intertidal zone—have the ability to take up
CHCs from their substrate (see Appendix HH). Of the dis-
posal options for Baltimore Harbor materials considered here,
only salt marsh creation and possibly island construction
would place dredged materials in the intertidal zone. These
are therefore the options where CHC uptake by emergent
grasses would be most likely.
5. Terrestrial Plants. Terrestrial plants may have
the ability to take up CHCs from their soil. Of the disposal
options for Baltimore Harbor materials considered here, new
terrestrial land will be created only in island creation and
upland disposal. Terrestrial plants are most likely to take
up CHCs from dredged materials at these locations.
202
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