CBP/TRS 129/94
Contaminant Trace Element Loads at
  the Susquehanna River Fall Line
       during the Spring, 1993
          High Flow Event

Addendum to the Fall Line Toxics 1992 Final Report
     Chesapeake Bay Program
                                   Of recycltd paptr

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 Contaminant Trace Element Loads at the
 Susquehanna River Fall Line during the
      Spring, 1993 High Flow Event

Addendum to the Fall Line Toxics 1992 Final Report
  Printed by the U.S. Environmental Protection Agency for the Chesapeake Bay Program

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Contaminant Trace Element Loads
at the Susquehanna River Fall Line
during the Spring, 1993, High Flow Event
Addendum to the Fall Line Toxics 1992 Final Report
prepared by: the Maryland Department of Environment
and: the U.S. Geological Survey, Department of the Interior
for the: IJSEPA Chesapeake Bay Program Office
INTRODUCTION
The largest freshwater discharge event on record to the Chesapeake Bay occurred
in the spring of 1993 as a result of several climatological factors. In 1993, as much as 92
inches of snow was recorded for the winter in some parts of the upper Susquehanna River
watershed. This snowpack was washed out by a single strong rainstorm that lasted
approximately nine days. The average precipitation for this storm in the basin above
Harrisburg was 7.5 inches. The total storinflaw for the Susquehanna River from this
storm exceeded that of the flow from Hurricane Agnes, a devastating storm that occurred
in 1973. Peak flow measured at Conowingo Dam during the spring storm event of 1993
was 500,000 cubic feet per second (cfs), approximately half of peak flow measured for
Hurricane Agnes (1,130,000 cfs). However, because of its longer duration and the larger
residual of stored water in the watershed, the 1993 storm transported a total of 816
billion cubic feet of water through the Conowingo Dam, compared to Hurricane Agnes’
total discharge of 521 billion cubic feet. During both storm events, a significant quantity
of sediment material, including the associated trace element contaminants, was
transported into the Bay from the watershed. In order to study the dynamics of
contaminant transport and to calculate accurate loads during this period of high flow in
1993, the United States Geological Survey (USGS) conducted a short-term intensive
water quality sampling study on the Susquehanna River at the Conowingo Dam in
Maryland.
The Susquehanna River is the largest tributary to the Chesapeake Bay,
contributing approximately 50% of the freshwater inflow to the Bay. It drains an area
that is impacted heavily by agriculture, and coal and mineral mining industries.
Additionally there is a significant number of municipalities that discharge effluents into
the Susquehanna River. There are therefore significant sources of trace element
contaminants from the Susquehanna watershed and mobilization of these to the
Chesapeake Bay can be strongly enhanced during a large storm event. A second and also
potentially important reservoir of trace element contaminants is stored in the sediments
behind each of the three dams in the lower Susquehanna River. These are, in order of
upstream to downstream, Safe Harbor, Hoitwood, and Conowingo. During high
discharge, scouring of stored sediments behind each dam can occur. According to Lloyd
Reed of the U.S. Geological Survey, (personal communication, 1993), scouring occurs at
the Conowingo Dam when discharge exceeds 200,000 cfs. This discharge level was
exceeded during most of the storm event in March/April, 1993.
METHODS
Water samples were collected at the Conowingo Dam site during March 25
through May 4, 1993. Samples were collected using ultra-clean techniques two to three
times per day for the nine day period of highest flow (March 25 - April 3, 1993), and an
1

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additional 11 times for the remaining 32 days of high flow. Samples were analyzed for
suspended sediment, dissolved aluminum (Al), and total-recoverable and dissolved
fractions of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), mercury
(Hg), nickel (Ni), lead (Pb), strontium (Sr), and zinc (Zn). Data for this study are in the
Appendix to this Addendum, entitled 1993 Trace Element Data for the Susquchanna
River at Conowingo Dam, MD. Loads of trace elements are calculated with a log-linear
regression model that fits parameters for discharge, time, and seasonality to the
concentration data. When there is not a significant relationship between the parameters
of the regression model, loads are calculated by the Interpolation/Integration (II) model
that interpolates concentration data, multiplies these by daily mean discharge
measurements, and then integrates over the year. Methodologies for sampling and
analysis are described in detail in the Fall Line Toxics Program 1992 Final Report.
RESULTS
Figure 1 presents a time series plot for discharge and suspended sediment
measurements at Conowingo Dam, MD, for the period covering 1992 and 1993. The
maximum discharge occurred in the spring of each year. However the plot also
emphasizes that discharge was much higher in the spring 1993 than in 1992, and that
storms which generate high discharges are an important mechanism for the mobilization
of sediments. Concentration data for total-recoverable and dissolved Pb and Zn during
this time period are presented in similar format in Figures 2 and 3, respectively. These
two trace elements are normally associated with the particulate phase of surface water
and therefore concentrations of total-recoverable Pb and Zn are correlated to discharge;
particularly during the spring storm events. During base flow, total-recoverable
concentrations of these 2 elements vary within a small range around the reporting limits
of this study. Dissolved concentrations of Pb and Zn do not show a correlation to
discharge or seasonality.
Figure 4 presents the time series plot for discharge and the concentrations of
dissolved and total-recoverable Cr at Conowingo Dam in 1993. There appears to be no
relation between discharge or seasonality with either phase of Cr.
Interestingly enough, the concentration of total-recoverable Cu exhibits a dual
behavior at the Conowingo site. Figure 5(a) presents the time series plot for dissolved
and total-recoverable Cu. During most of this time period, there was no more than a
minimal correlation between discharge and total-recoverable Cu concentration (R=O.79
for the entire two year period). In fact there are several base flow concentration values
that fail within the mid- to upper-range of stormflow data. However, during the storm
event in late March and April, 1993, the behavior of Cu concentration changes and
follows the discharge profile very closely. Figure 5(b), which is an expanded version of
the 1993 storm event portion of the time series, emphasizes this point. The average total-
recoverable Cu concentration was also slightly higher during this storm event than for
base flow in 1993; 4.09 ± 1.97 (1 S.D.) as compared to 2.53 ± 1.51. The data suggest that
total-recoverable Cu concentration is not related to discharge rates, except during
abnormally high stormflows. There were no discernible relationships or trends for
dissolved Cu during this study period.
Quality control data for all the trace elements presented in this addendum are
given in the Fall Line Toxics Program 1992 Final Report. Briefly, all blank data for
total-recoverable Cu, Pb, and Zn were less than the reporting limit. Dissolved blank data
for these trace elements had measurable concentrations, but with values significantly less
2

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Discharge and
at Conowingo
Suspended Sediment
Dam, Maryland
400000 D
C l )
C)
300000
CD
200000
100000
0
Dec
Mar
Jun
1992
Sep Dec Mar
Figure 1. Time series of suspended sediment concentration
Conowingo Dam, MD for the time period from 1992 to 1993.
Jun Sep Dec
1993
and instantaneous discharge for the Susquehanna River at
250
-J
a)
E
C
C
0
CD
I -.
C
C)
0
C
0
C-)
500000
200
150
1 00
50
0
3

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Total Recover.able and Dissolved Lead
at Conowingo Dam, Maryland
Dec Mar
Jun Sep
1992
Figure 2. Time series of total-recoverable (tot.-rec.) and dissolved Pb
Susquehanna River at Conowingo Dam, MD for the time period from
dissolved Pb are 1.0 and 0.06 tg/L, respectively.
Jun Sep
1993
Dec
500000
400000 D
CR
C)
300000 ca
CD
200000
100000
0
(aq.) concentrations and instantaneous discharge for the
1992 to 1993. Reporting limits for total-recoverable and
-J
a)
a
C
C
0
CO
I -.
C
w
0
C
0
C-)
15
10
5
0
Dec Mar
4

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Total-Recoverable and
at Conowingo
Dissolved
Dam, Maryland
Zinc
400000
300000
200000
100000
0
Dec Mar
Jun Sep
1992
Jun Sep
1993
Figure 3. Time series of total-recoverable (tot.-rec.)
Susquehanna River at Conowingo Dam, MD.
respectively.
and dissolved (aq.) Zn concentrations and instantaneous discharge for the
Reporting limits for total-recoverable and dissolved Zn are 10 and 0.08 tg/L,
100
C)
a
500000
0
Cu
1
C
U)
U
C
0
()
80
60
40
20
0
Dec Mar
Dec
5

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Total-Recoverable
at Conowingo
and Dissolved Chromium
Dam, Maryland
Aug Oct Dec
400000 9
(I )
C,
a)
300000
200000 2
U)
100000
0
Figure 4. Time series of total-recoverable (tot.-rec.) and
Susquehanna River at Conowingo Dam, MD for 1993.
.tgfL, respectively.
dissolved (aq.) Cr concentrations and instantaneous discharge for the
Reporting limits for total-recoverable and dissolved Cr are 1 and 0.2
6
-j
0)
a
C
C
0
I-
C
0
0
C
0
U
500000
5
4
3
2
1
0
Dec
Feb
Apr
Jun
1993
6

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(a) Total-Recoverable and Dissolved Cu
for 1992 to 1993
Mar Jun Aug
1992
(b) Total-Recoverable
during the 1993
March
Sep Dec
Cu and Discharge
Storm Event
May
Figure 5. Time series of total-recoverable and dissolved Cu and instantaneous discharge
for the Susquehanna River at Conowingo Dam for (a) 1992 to 1993 and (b) during the
spring storm event of 1993. Reporting limits for total-recoverable and dissolved Cu are 1
and 0.02 p.gfL, respectively.
-J
a
C
0
C
0
U
C
0
C.)
-I
a
C
C
0
C
0
C.)
C
0
C.)
10
8
6
4
2
0
.10
8
6
4
2
0
Nov Jan Apr Jul
1993
500000
400000 D
C)
300000 c
0
200000 C)
100000
0
500000
400000 C
U)
C)
U)
300000
0
200000 C)
U)
100000
0
April
7

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than the environmental data. Quality control data for Cr indicated that contamination by
this element may have occurred in 1992 and in part of 1993.
DISCUSSION
Trace Element Concentrations
Much of the trace element concentration data collected during the storm event of
1993 exhibited predictable behavior related to the elevated suspended sediment loads.
The elements Pb and Zn are examples of soft-metal trace-element contaminants that are
easily scavenged onto particulate surfaces. Sources of the contaminated suspended
sediments during a storm event include runoff from the watershed as well as scouring of
stored sediments from behind the dams of the lower Susquehanna River. During high
flow, scouring is probably a significant source of sediment with trace elements sorbed to
it. Data for Al and Fe concentrations, presented in the Appendix, also correlate well to
suspended sediment loads.
The environmental geochemistry of Cr in this system is not obvious from the
results of this study. Sources of Cr to the Susquehanna River are probably primarily
industrial or atmospheric deposition. It is not obvious from the data that Cr is being
stored in sediments behind the Conowingo Dam, or that storms in general have a major
influence on the behavior of this trace element. More study is required for better
understanding of the geochemical behavior of Cr.
The dual behavior of total-recoverable Cu in 1993 at Conowingo Dam suggests
that there are multiple sources of this trace element in the Susquehanna watershed.
During base flow, Cu sources may include drainage from active or abandoned coal and
mineral mining operations, and industrial effluents such as from the steel and iron
industries. During stormflow, it is possible that the Cu concentration is being augmented
by sediments scoured from behind the darn, but if this were a significant source of Cu,
one would expect to see elevated Cu concentrations whenever discharge was high enough
to induce sediment scouring. While scouring occurred during almost the entire high
stormflow period, from March 25 through April 28, most of the Cu concentrations for
this period were within the range of base flow concentrations. There were five points that
exceeded this range and these occurred only during the first three days, when peak flow
occurred in 1993 storm event. The induction of a different source of Cu, other than
sediment scouring, during abnormally high stormflow provides a better explanation for
elevated concentrations and the unusual relationship to discharge during this storm event.
The most likely alternate source is from municipal effluents.
Municipal effluents, contaminated from Cu plumbing used for water supplies,
have been suggested as a general source of this trace element into river systems.
However, since many of the sewage treatment plants in the Susquehanna River watershed
have recently installed secondary treatment, municipal effluents are probably not a
primary source of Cu during base flow. This is not necessarily the case for stormflow.
Many of the municipal sewage treatment plants in the Susquehanna watershed have
combined sewage treatment, in other words they combine storm drain effluents with
municipal sewage. Treatment plants can become overwhelmed during unusually high
flow, such as occurred in the spring of 1993, and be forced to discharge raw sewage
directly into the Susquehanna River or its tributaries. Under very high flow regimes, Cu
becomes correlated to discharge, and this may be related to the municipal overflows
during storm surges. This would also explain the slightly higher Cu measurements that
occurred at the peak flow of the storm event.
8

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Concentration data for the other trace elements, As and Cd, were consistently
below detection limit, so interpretation of theft geochemical behavior during the 1993
storm event is not possible.
Load Estimates
Concentration data collected and mean daily discharges for river flow throughout
1993 were used to estimate annual loads of contaminant trace elements for that year.
These load data are presented in Table 1.
Table 1. Annual loads of total-recoverable and dissolved trace elements for the
Susquehanna River at Conowingo Dam, MD. Units are in metric tons per year. Lead
values in italics were calculated with the Integration/Interpolation model (11). For
constituents using the H model with censored data (measured concentrations less than the
reporting limit), the load estimates were calculated twic&to determine a range in values.
Censored data were assigned a value of zero for the calculation of a lower boundary or
“minimum load,” and a value of the analytical reporting limit for the calculation of an
upper boundary, or “maximum load.” All other load estimates (in normal print) are
calculated with the log linear regression model (AMLE, Cohn) and ranges in loads are
statistical estimates of variance (± 1 standard deviation) made by the model. Both models
are described in detail in the Fall Line Toxics Program, 1992 Final Report.
The upper ranges of annual load estimates for total-recoverable Cr, Cu, Pb, and
Zn are presented in bar graph format in Figure 6. For comparison, load estimates for
1992 are included hi this graph. The spring portion (March, April, and May) of the
annual load for each trace element is indicated as the stippled portion of each bar to
evaluate the relative contribution of the large storm event to the annual load. Total loads
for Cr, Cu, Pb, and Zn in the Susquehanna River at Conowingo Dam were consistently
higher in 1993 than in 1992. The differences between the spring contributions of loads
for each year are, however, more significant. For example, the spring contribution of the
total annual Zn load delivered to the Chesapeake Bay in 1992 was 37% of the total
annual load, while in 1993, a more significant 70% of the annual Zn load was transported
in the spring. This same phenomenon was demonstrated for all of the other total-
recoverable loads, and demonstrates the importance of stormilow to annual contaminant
loads. The increased contaminant loads from the spring storm event of 1993 can be
partially attributed to elevated concentrations of the contaminants, but more importantly
to the large volume of water that was discharged from the watershed.
9

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Annual
Loads of Contaminant Trace Elements
at Conowingo
Dam, Maryland
Pb
0
1992 1993 1992 1993 1992 1993 1992 1993
Figure 6. Annual load estimates of total-recoverable Cr, Cu, Pb, and Zn for the Susquehanna River at Conowingo Dam, MD.
The spring contribution of each load (March, April, and May) is indicated as the stippled portion of each bar.
U)
C
0
C)
I-
C)
E
1200
1000
800
600
400
200
0
C
C
Cr Cu
E.:...:.::.,.::.: I _____ _____
10

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CONCLUSIONS
The results of this swdy suggest the following conclusions:
(1) Contaminant concentrations of trace elements that are associated with particulate
phases, for example Pb and Zn, are correlated with discharge, particularly during
very large storm events such as occurred in the spring of 1993.
(2) The concentration behavior of Cu is more complex than for some of the other
trace elements, having multiple sources that are apparently similar in importance.
(3) Scouring of stored sediments from behind the Conowingo Dam may contribute
significantly to the suspended sediment load, and hence contaminant trace
element loads of Pb and Zn.
(4) All annual load estimates for 1993 were higher than had been observed in 1992.
This was at least partially due to the large volume of water that was transported
during the spring stormilow of 1993, and a disproportionately large fraction of the
annual load was contributed during this storm event.
11

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APPENDIX
1993 TRACE ELEMENT DATA FOR THE SUSQUEHANNA RiVER
AT CONOWINGO DAM, MD
12

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SUSQUEHANNA R AT CONOWINGO. MD
SEDI- SED CHRO-
1IENT SUSP. ALUM- CADMIUM CHRO- MIUM COPPER
DIS- SIEVE INUM. ARSENIC CADMIUM TOTAL MIUM, TOTAL COPI’ER, T iAL
CHARGE, DIAN. DIS- DIS- ARSENIC DIS- R!COV- DIS- RECOV- DIS- RZCOV-
SUS- I FINER SOLVED SOLVED TOTAL SOLVED ERABLE SOLVED ERABLE SOLVED ERABLE
DATE PENDED THAN (UG/L (UG/L (UG/L CUG/L (UG/L (UG/L (UG/L (UG/L (UG/L
CT/DAY) .062 t41 AS AL) AS AS) AS AS) AS CD) AS CD) AS CR) AS CR) AS CU) AS CU)
(80155) (70331) (01106) (01000) (01002) (01025) (01027) (01030) (01034) (01040) (01042)
WATER-QUALITY DATA. CAI.ENDAR YEAR JANUARY 1993 TO DECEMBER 1993
DIS- BARO- SPE- PU ALKA-
CHARGE. METRIC SPE- CIFIC WATER UNITY
INST. PRES- CIFIC CON- WHOLE WAT DIS SEDI-
CUBIC TEMPER- TEMPER- SURE CON- DUCT- OXYGEN, FIELD TOT IT MENT,
FEET ATURE ATURE ( tl DUCT- A liCE DIS- (STAND- FIELD SUS-
DATE TIME PER WATER AIR OF AliCE LAB SOLVED AND /L AS FENDED
SECOND (DEG C) (DEG C) HG) (US/CM) (US/CM) (MG/L) UNITS) CACO3 ( /L)
(00061) (00010) (00020) (00025) (00095) (90095) (00300) (00400) (39086) (80154)
JAN
05...
07...
08...
20...
MAR
11. .
25...
27...
28...
30...
31...
31...
1430
1330
1300
1130
1400
1130
1245
1330
1645
0145
1400
95900
101000
114000
69200
70900
145000
162000
184000
314000
321000
415000
5.0
5.0
6.0
5.5
4.0
5.0
6.0
7.0
7.0
7.0
8.0
18.0
13.0
9.0
7.0
10.0
9.0
11.0
15.0
16.0
8.0
15.0
742
769
766
774
‘
763
771
766
759
757
761
759
138
171
163
219
290
270
225
220
160
165
146
155
150
154
201
255
258
207
202
154
149
132
13.0
13.3
12.9
13.9
12.5
13.0
13.2
12.7
——
12.5
12.3
——
7.4
7.9
7.8

7.3
7.3
7.5
7.3
7.3
7.2
7.2
——
26
27
28
31
45
25
31
17
25
20
25
14
18
7
14
21
32
28
79
67
97
APR
01...
01. .
02 .
03 . .
03...
03...
03.
04 .
04..
05 .
08
12. .
13 .
15...
19 . .
22...
28 .
1230
2300
1315
1030
1715
1900
2230
1230
1945
1230
1500
1545
1415
1045
1515
1515
1115
448000
431000
480000
477000
461000
460000
430000
404000
378000
326000
190000
337000
295000
207000
300000
193000
244000
6.0 11.0
7.0 14.0
7.0 12.0
7.0 12.0
—— ——
6.0 6.0
-— -—
7.0 10.0
7.0 8.0
7.0 15.0
9.0 16.0
8.0 14.0
10.0 19.0
9 0 16.0
12.0 22.0
12.0 8.0
11.0 20.0
749
749
752
762
——
763

765
764
766
763
753
759
760
759
747
771
128
120
114
119
——
116
220
114
124
172
196
128
133
148
——
174
118
116
115
109
—
111
111
111
116
151
147
118
129
134
150
156
12.7
12.5
12.0
12.6
11.7
13.2
12.8
13.3
12.9
12.5
12.6
10.8
11.9
11.1
11.9
7.3
7 2
7.0
7.0
“
7.1
7.2
7.3
7.4
7.5
7.3
7 4
7.4
7.5
——
7.5
-—
-—
——
20
12
20
17
19
19
23
21
26
29
22
23
28
32
91
338
214
251
230
234
167
175
177
131
28
95
118
99
92
46
50
MAY
03...
JUN
09 . .
23
1215
1130
1330
121000
6700
46900
16.0
23.0
28.0
23.0
28.0
37.0
770
760
766
178
337
385
167
318
——
10.3
6.1
5.4
7 3
7.5
7.9
-—
31
66
15
8
JUL
07...
28
0915
0945
6400
5960
29.0
30.0
35.0
34.0
767
762
395
366
359
350
5.5
4.5
7.7
7.4
68
78
7
JAIl
05...
6470
99
30
<0.60
<1
0.16
<1
1.90
5
1.47
2
07
08 ..
3820
5540
100
96
30
20
——
<0.60
-—
<1
——
0.10
——
<1
——
0.63
——
——
-—
0 69
——
5
20 ..
1310
94
30
——
——
——
——
——
—-
-—
MAR
11 .
25 .
27...
28 ..
30...
31...
31
2680
8220
14000
13900
67000
58100
109000
99
96
96
98
99
99
98
30
30
<10
20
<10
<10
<10
-—
<0.60
<0.60
<0.60
<0.60
0.65
<0.60
<1
<1
<1
<1
<1
1
<1
—-
0.10
0.10
0.10
0.10
0.10
0.10
<1
<1
<1
<1
<1
<1
<1
—-
<0.20
0.36
0 59
<0.20
<0.20
<0.20
<1
<1
1
1
3
<1
5
--
0 74
1.49
0.79
1.24
0 36
0.39
2
<1
2
2
4
4
3
APR
01 . .
01
02 . .
03
03...
03.
03 .
04..
04 .
05 .
08
12
13 .
15.
19 .
22 .
28...
110000
393000
277000
323000
286000
291000
194000
191000
181000
115000
14400
86400
94000
55300
74500
24000
32900
98
97
97
97
97
97
98
95
94
92
97
92
96
99
97
99
96
<10
<10
<10
<10
“
20
-—
40
20
10
20
30
10
40
30
20
20
<0.60
<0.60
<0.60
0.88
1.03
—-
<0.60
<0.60
<0.60
<0.60
<0.60
<0.60
<0.60
<0 60
<0.60
<0.60
1
2
2
2
“
2
—-
1
2
1
<1
<1
1
1
<1
<1
<1
0.10
0.10
0.10
0.10
0.10
——
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.10
<1
<1
<1
<1

Cl
——
Cl
Cl
Cl
<1
<1
<1
<1
<1
<1
<1
<0.20
<0.20
0.65
<0.20
<0.20
——
<0.20
0 35
<0.20
<0.20
<0.20
<0.20
<0.20
<0.20
0.44
0.46
1
6
4
3
5
-—
4
2
1
<1
2
1
4
1
——
<1
0 30
0.66
0 90
0.42
“
0 50
0 41
0 64
0.44
0.70
0.81
0.90
0.59
1.08
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