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Effluent Concentration Patterns in Tennessee River
Below the Waste-Treatment Outfall from
Monsanto's Decatur, Alabama Plant
Prepared byJ. M. Lawrence, Professor
Department of Fisheries and Allied AquaculturesAgricultural Experiment Station
Auburn University, Alabama 36849
October, 1980
Introduction
In August 1980, Rhodamine B dye was used to determine the flow pat-
terns in the Tennessee River of the effluent released from the Monsanto
Plant waste-treatment outfall located in Decatur, Alabama. The objective
of the study was to establish the dilution pattern of the waste in the
Tennessee River. The patterns were monitored within a 2,000 m stretch
of the river below the waste outfall.
Studies were conducted on the 19th and 20th of August. Weather con-
ditions were similar each day with clear skies, a constant North-North-
westerly wind of 6+ mph, and air temperatures in the mid 90's. Water
temperatures ranged from 300e at the 8 m depth to 310e at the surface.
Dissolved oxygen ranged from 4.5 ppm at 8 m to 6 ppm at the surface.
River flow during the dye monitoring periods was dependent on the
discharge from the hydroelectric plants at Guntersville and Wheeler
Dams. On 19 August, river flow was noticeable throughout the monitoring
period, while on 20 August, river flow was reduced during the first half
of the monitoring period. Flow did increase during the last half of
this period. Effluent flow rates were approximately 2,800 gallons per
minute (gpm) throughout each study period.
First Monitoring Period1600-2045 hours - 19 August 1980
A total of 7.5 gallons of Rhodamine B dye was injected into the
effluent line at its origin below the treatment lagoons between 1530
and 1630 hours on the 19 August. The dye was well mixed with the
effluent before its release from the discharge pipe into the river.
1
,•
Monitoring of the dyed effluent began at 1600 hours. A sample
of the dyed effluent was collected immediately downstream of the
outfall at a depth of 6 to 7 m. This sample was the 100 percent
concentration reference for determining downstream dilutions.
Along the 2000 m stretch of river studied, several cross-sectional
samples were run to determine the width and depth of various concen
tration isopleths(Table 1). These samples were run between 1600
and 2045 hours. The depths sampled at each vertical profile were
0, 2, 4, 6, and 8 m or fraction thereof to the river bottom.
Table 1. The location of cross section samples and the number ofvertical samples run per cross section.
Station Location No. vertical samples/crosssection
a1234567
Immediately below discharge pipe50 m below station a100 m below station a250 m below station a500 m below station a1000 m below station a1500 m below station a2000 m below station a
13444534
An illustrated description of the first dye cloud is given in
Figure 1 (6+ m depth), Figure 2 (2 to 6 m depth), and Figure 3 (0 to 2 m
depth). The cumulative areas and volumes (downstream from the outfall)
within a given concentration isopleth are provided in Table 2. Samples
were analyzed using a flow-through type fluorometer.
2
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MONSANTO'S OICATUI At "lANT
Figure 1. Point A = discharge outlet; point B = 500 m; point C = 1,000 m; point D = 1,500 m. Area of dye cloud = 18.3acres, volume = 150 acre feet.
l.t· ..I.~ I.;.,1I~I~L~
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MONSlNTO'S OIC"TUI ll.IOL, ... T
"-.......
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Figure 2. Point A = discharge outlet; point B = 500 m; point C = 1,000 m; point 0acres, volume = 429 acre feet.
1,500 m. Area of dye cloud = 32.7
1_- ~ ..... ",,1, 1I~11u........"',~
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6 • .,.
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1000 'O"'S h .. AUliI l'J lOla
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101 ..
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MONSAN10S OleA1UI Al. "lANI
-".... ~
....... B
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Figure 3. Point A = discharge outlet; point B = 500 m; point C = 1,000 m; point 0 = 1,500 m. Area of dye cloud = 93acres, volume = 610 acre feet.
Ii. 1I~1lJ,.·
Table 2. Cumulative area and volume occupied by Rhodamine B dye inTennessee River adjacent to Monsanto's Decatur, AL Plant between 1600 and 2045 hrs. on Aug. 19 and 0945 and 1335 hrs. onAug. 20, 1980.
Effluent con- August 19 Pattern August 20 Patterncentration inri ver water Cumulative Cumulative Cumulative Cumulative
Area Volume Area Volume(percent) (acres) (acre feet) (acres) (acre feet)
40 0.34 2.8
30 1.85 15.4 0.30 2.7
20 2.86 23.6 0.60 5.0
10 6.54 53.6 1.00 8.3
5-9 8.21 67.8 2.67 24.8
1-4 22.04 209.8 18.76 154.9
.5-.99 90.07 690.2 81.82 668.8
.5 144.lD 1,188.9 145.93 1. 287.5
Tota1 144.10 1,188.9 145.93 1.287.5
6
Second Monitoring Period1000-1335 hours 20 August 1980
A total of 6 gallons of Rhodamine B dye was injected into the
discharge line at its origin below the treatment lagoons between 0945
and 1030 hours on 20 August.
Monitoring of the dyed effluent in the Tennessee River was started
at 1000 hours, and utilized the same techniques as outlined for the first
monitoring period. Cross-sectional sampling of the dye cloud was
conducted between 1000 and 1335 hours at the same stations and depths
utilized during the first monitoring period.
An illustrated description of the second dye cloud is provided
in Figure 4(6+ m depth), Figure 5 (2 to 6 m depth), and Figure 6
(0 to 2 m depth). The cum~ative areas and volumes within a given
concentration isopleth are provided in Table 2.
Discussion
This same section of the Tennessee River below the Monsanto
Plant's waste-treatment outfall was studied on 9 October 1976. At
that time the water level of Wheeler Reservoir was down 4+ feet in
preparation for collecting winter rains. The water temperature was
190 C. The Rhodamine B dye, introduced into the effluent line immed-
iately below the lagoon, surfaced immediately upon its release from
the outfall pipe into the river. The dye cloud flowed along the old
river channel, which is the area of waterfront occupied by two parallel
rows of mooring piers used by barges servicing the Monsanto plant.
This cloud was confined to the area along the south bank of the river
for the next 1.5 miles downstream.
7
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ITl H'. 'un...
••• ..,1111'" 1115..,. h. II 1111
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..--- - - k-- _----~./".-,r...-"-.-=-~,..,-
\ MONSANTO" OICATUI Al. ~lAHT
•
Figure 4. Point A = discharge outlet; point B = 500 01; point C = 1,000 01; point 0 = 1,500 m. Area of dye cloud= 23.3 acres, volume = 191 acre feet.
... .. JI' :,.;':"~ ..1l1111~__'::"'~u-'*
u,
~ONS"'NTO S DICA'UI AL PLANT
Figure 5. Point A = discharge outlet; point B = 500 m; point C = 1,000 m; point D = 1,500 m. Area of dye cloud= 44.4 acres, volume = 583 acre feet.
Til ... ,+301
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"'0' C,."
01'1 HOW 'ATTI'N5
0·1 ....hpth
lOU UB It ...... i.!O 1110
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B
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100 ...
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MON,ANTO S OleA TV' AL 'lANT
, - Q;"
~ A
••••··
Fi gure 6, Point A = discharge outlet; point B = 500 m; point C = 1,000 m; point 0 = 1,500 m. Area of dye cloud= 78,2 acres, volume = 513 acre feet,
""
The apparent cause of the dyed effluent surfacing immediately upon
its release into the bottom waters of the river was that the effluent
was several degrees warmer than the river water. Confinement of the
cloud to the old river channel occurred because of the shallow depth
(0 to 1+ feet) of water over the old south river bank. This restricted
diffusion of the dyed waters into the flat area to a concentration near
zero.
First Dye Cloud, 19 August 1980
Prior to the introduction of the Rhodamine B dye into the effluent
pipe it had been anticipated that the dyed effluent released at the
outfall would again surface immediately. This did not occur and since
the exact location of the mouth of the outfall pipe was unknown, con
siderable effort was expended locating the release area of assumed
100 percent concentration for this study. The point of collection for
the 100% sample was probably a few feet downstream of the actllal
release point of the effluent, so the dye was more dilute than when
it was released from the outfall pipe. Since the concentration of the
effluent at the release point was greater than the 100% reference
sample, all of the implicated concentration isopleths plotted should
move upstream.
As indicated in Figure 1, the major concentration of the dyed
effluent maintained a relatively narrow cloud at the 6+ m depth along
the south bank for some 1,500 m downstream. The time required for the
leading edge of this cloud to travel this distance was 4 plus hours.
At the 6+ m depth the dilution ranged from 100% at the outfall to less
than 0.1 %at 1,500 m.
11
The 2 to 6 m dye cloud started approximately 50 m below the outfall
and maintained a relatively confined pattern between the 2 rows of piers
for 300 m downstream. This cloud continued to hug the old river bank
in a narrow band for the next 1,200 m. Dilution in the dye cloud
ranged from about 8% near the most upstream mooring pier to less than
0.1 % approximately 1,500 m downstream.
Deepening of the river bank in front of the water circulating pumps
allowed a portion of this dye cloud to be circulated through the cooling
system of the plant.
The a to 2 m dye cloud emerged to the surface approximately 450 m
downstream of the effluent outfall. It spread outward from the bank
into the river for a limited distance, but the northernly wind pushed
the cloud over the shallow flat between the river and the two cooling
water outfalls. This action plus pump circulation of dyed waters pro
duced considerable dye coverage in this shallow water area. Downstream
of the State Dock barge canal the dyed waters spread into the river
channel, but diffusion into the southerly flats was extremely limited.
The area occupied by the first dye cloud was 144.1 acres and the
total water volume within this affected area was 1,188.9 acre feet.
Second Dye Cloud, August 20, 1980
The collection of the 100 percent discharge effluent sample for moni
toring the second dye cloud probably came from a point a few feet down
stream of the outfall mouth. Consequently, the concentration of dyed
effluent had been slightly diluted by river water. However, calculations
of other downstream concentrations were based upon this sample being the
100 percent reference solution.
12
As indicated in Figure 4, the dye cloud for the 6+ m depth maintained
a fairly narrow concentrated flow along the south bank on the river bot
tom, but due to the reduced river current, there was considerably more
horizontal diffusion than had occurred during the August 19 study. Dur
ing the 3 hours and 35 minutes of study this cloud moved some 1,300 m.
Concentrations of dye within this cloud ranged from 100 percent at the
outfall to 0.1 percent at the mouth of the State Dock barge canal.
The 2-6 m depth dye cloud originated near the most upstream chemical
mooring pier and dispersed over a wider area along the south river bank
than had occurred with the first cloud on August 19. The concentrations
of dye in this 2-6 m depth cloud ranged from 5 percent in the mid-section
of the mooring pier area to 0.1 percent some 1,300 m downstream.
The 0-2 m dye cloud (Figure 6) originated at the upstream chemical
mooring pier and spread over a considerable area both north and south of
the mooring pier area. There was a slight upwelling of the dye concen
tration in the vicinity of the pump intake indicating their withdrawal
had created a current during the low river flow interval of the study
period. As a result of this, the release of dyed water by the two heated
water outfalls produced a rather extensive cloud over this shallow water
area. The northerly wind also tended to push the surface dye cloud over
this shallow water area.
The total area covered by this dye cloud was 145.9 acres and the total
water volume within this area was 1,287.5 acre feet.
13
Summary
Personnel of the Auburn University Fisheries Department have been in
volved in three dye studies of Monsanto's Decatur, Alabama treatment la
goon effluent dispersion in the Tennessee River.
The first study conducted October 9, 1976 was during a period when
the water level of Wheeler Reservoir was down 4+ feet in preparation for
its winter pool elevation, and the water temperature was 19oC. Data on
dye dispersion indicated that the effluent was fairly uniformly distri
buted from top to bottom along the old river channel from the mouth of
the outfall to a point some 2,500 m downstream. However, that study in
dicated that the greatest concentration of dye was more or less confined
to the area between the two rows of mooring piers immediately downstream
of the outfall.
The second study was conducted on August 19, 1980 when the reservoir
was at full pool, hydrodischarge was producing a current, and the water
temperature ranged from 30-310 C. The dye cloud obtained at this time
maintained the same general pattern along the south bank of the Tennessee
River, but the heaviest concentration of dye was in the 6+ m depth layer
of water. The released dye did not surface until the cloud had travelled
some 450 m.
The third dye study was conducted on August 20, 1980 when the reser
voir was at full pool, water temperature was 30-310 C and for approximately
half of the study period the river flow was greatly reduced. The dye
cloud dispersed from the bottom to the surface within 100 m of the outfall.
The cloud at the 6+ m depth was concentrated in a narrow band along the
south river bank. In the shallow water, the dye diffused north and south
of this narrow band, probably because of restricted flow. From the pump
14
area downstream the dye cloud concentrated over the shallow area imme
diately adjacent to heated water outfalls.
Based upon studies of the 3 dye clouds formed and the vertical as
well as horizontal concentrations of dye within each cloud produced by
outfall released dye effluent from Monsanto's Decatur, Alabama treatment
lagoons, the released effluent disperses in the following patterns.
During hot weather with a full reservoir and normal river flow, the
major portion of released effluent tends to concentrate near the river
bottom (6+ m depth) adjacent to the south bank. For the first 300 m
downstream of the outfall the effluent flowed between the two rows of
mooring piers. Within 500 m downstream of outfall the effluent was dilu
ted to 20 percent of its released concentration, and within 1,000 m it
was diluted to 10 percent of its released strength. Surface dilution at
1,000 mwould generally be 1 percent or less. Dispersion of the effluent
into surface waters occurred at the downstream end of the parallel rows
of mooring piers.
During hot weather with slack water conditions (under reduced hydro
electric generation) the released effluent follows along the river bottom
between the 2 rows of mooring piers. Under these low flow conditions
dispersion of effluent into shallower depths, including the surface waters,
occurs within this pier area. From the vicinity of the pump station
(which is approximately 500 m downstream of outfall) the effluent concen
tration is fairly uniform from surface to bottom of river, and with
northerly winds may become dispersed over the shallow water areas in the
vicinity of heated water outfalls. The pumps also help disperse the
diluted (1 percent of outfall concentration) effluent over this shallow
15
area. From 1,000 m + downstream the effluent concentration is less than
1 percent, and at 2,000 m is less than 0.1 percent.
Under cool or cold weather conditions (from 1976 data) the released
effluent immediately disperses itself from the river bottom to surface
by the time it flows to the mooring pier area. It flows through these
piers and tends to be restricted to the area along south bank of old
river channel since the drawdown allows a partial barrier to be formed
between old river channel and shallow areas adjacent to heated water
outfalls. Durin9 such periods the pumps may cause some circulation of
dilute effluent-laden waters into the shallow water areas. A northerly
wind will cause this dilute (1 percent or less) effluent to disperse
over shallow water areas downstream of pumps section. The cooling water
pumps will also circulate these dilute (1 percent or less) effluent-laden
waters over these shallow areas.
If one considers the entire volume of the old river channel for the
distances included in these two August, 1980 studies, Monsanto's released
effluent would occupy less than 22 percent of this river segment.
16
APPENDIX
17
APPENDIX TABLE 1
Cumulative area and volume within each concentration level for the6+ m depth, the 2-6 m depth, and the 0-2 m depth for study
conducted on August 19, 1980.
Cumulativeeffl uentconcentration(percent)
6+ mCumulative
Area, Volume,acres acre feet
Depth2-6 m
CumulativeArea, Volume,acres acre feet
0-2 m
CumulativeArea, Volume,acres acre feet
40 0.34 2.8
30 1. 80 14.9 0.05 0.5
20 2.81 23.1
10 6.49 53.1
5 7.91 64.8 0.30 3.0
1 8.05 105.0 6.08 40.0
.5 8.57 70.2 13.08 171. 0 68.42 449.0 ,
. I 18.29 149.9 32.72 429.0 93.09 610.0
18
APPENDIX TABLE 2
Cumulative area and volume within each concentration level for the6+ m depth, the 2-6 m depth, and the 0-2 m depth for study
conducted on August 20, 1980.
Cumulativeeffl uentconcentration(percent)
6+ m
CumulativeArea, Volume,acres acre feet
Depth2-6 m
CumulativeArea, Volume,acres acre feet
0-2 m
CumulativeArea, Volume,acres acre feet
30
20
10
5
1
.5
.1
0.3
0.6
1.0
2.1
9.6
23.3
2.67
5.00
8.34
17.30
78.82
191. 10
0.57
4.31
17.75
44.45
19
7.46
56.63
233.01
583.38
12.35
54.47
78.19
81.0
357.0
513.0