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.

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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.

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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

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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.

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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.

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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.

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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.

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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,

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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