1
Dissolved Oxygen Variability in the Sangamon River in the Vicinity of the Decatur, Illinois Wastewater
Treatment Plant Discharge
Field Team
Larry D. Arnold, Jeff Runyon, Bill Cunningham
Dr. W.D. Hatfield Laboratories, Sanitary District of Decatur, 501 Dipper Lane, Decatur, IL 62522
Jared Harris
Engineering Department, Sanitary District of Decatur, 501 Dipper Lane, Decatur, IL 62522
Laboratory Analysis Support
Latishia Greve, Nancy Dudley
Introduction
The Sanitary District of Decatur is a municipal wastewater treatment plant providing service to
the city of Decatur, Illinois and several of the surrounding smaller municipalities. The plant has a design
average flow of 41.0 MGD and a design maximum flow of 125.0 MGD. The plant is capable of primary
treatment for solids removal, secondary treatment using an activated sludge process to remove
dissolved biodegradable organics, and has a seasonal (May through October) disinfection requirement
which is achieved using sodium hypochlorite solution to disinfect and a sodium bisulfate solution for
chlorine residual removal prior to discharge to the Sangamon River. The district also operates four
Combined Sewer Overflow facilities for primary treatment of excess flow during periods of excessive
rainfall and land applies it’s anaerobically treated biosolids after lagoon storage each fall.
One of the major factors affecting the compliance limits established for the district by the Illinois
EPA (IEPA) is the fact that the district treatment plant is located downstream from the Lake Decatur
dam. This means that at times there is minimal or no flow in the Sangamon River upstream from the
plant and the seven day once in ten year low flow (7Q10) is 0 cubic feet per second. This fact results in
the district’s effluent being subject to Illinois water quality standards as opposed to Effluent standards
whose concentration limits are substantially higher in most cases.
Among pollutants present in the district’s effluent for which current treatment processes are
inadequate to meet anticipated water quality standards in Illinois are total nitrogen and total
phosphorus. The IEPA has identified that dissolved oxygen (DO) and total nitrogen are potential causes
of impairment in Sangamon River segments downstream of the treatment plant that are on the 303 (d)
list of impaired waters(1). The IEPA is also currently evaluating establishing standards for the nutrients
phosphorus and nitrogen. In the next National Pollutant Discharge Elimination System (NPDES) permit
update cycle, the IEPA will be adding a requirement to monitor these parameters on a monthly basis.
They have already established DO limits which are currently present in the district’s NPDES permit.
One of the issues arising during the IEPA evaluation of these nutrient limits was the effect of
nutrients on DO levels in the receiving stream. The presence of excess nutrients can cause algal growth
2
which is reflected in DO “swings”. Over a diel (24-hour) cycle, supersaturated DO levels may occur
during the sunny part of the day when photosynthesis, and consequently DO production, would be
expected to be highest. Additionally, DO levels may occur in the early morning, which may be lower than
water quality standards for protection of aquatic life, due to the uptake of DO at night by aquatic life.
For determination of whether these conditions exist, continuous monitoring of the receiving stream for
DO and temperature (upon which DO concentration is dependent) is essential. The district decided to be
proactive and investigate whether such conditions exist in the Sangamon River within the areas of
influence of its effluent, during a summer low river flow period when dissolved oxygen levels are at their
lowest during any given calendar year.
Materials and Methods
1) YSI 6920 V@ Sonde with optical DO, Chlorophyll, Conductivity, and Temperature sensors with
EcoWatch software installed on Hewlett Packard Probook laptop computer.
2) Metal containment cage, heavy-duty cable, and padlocks for securing Sonde in river
3) Hip length waders
4) Appropriate sampling bottles for water quality analyses to be performed concurrent with start
and finish of in-river monitoring period for following methods :
a) DO by Method 4500-O C., Standard Methods for the Examination of Water and Wastewater,
19th ed.
b) Total Suspended Solids by Method 2540 D, Standard Methods for the Examination of Water
and Wastewater, 19th ed.
c) pH by Method 4500H+B, Standard Methods for the Examination of Water and Wastewater,
19th ed.
d) Metals by US EPA Method 200.7
e) Ammonia-Nitrogen by Method 4500-NH3 D, Standard Methods for the Examination of
Water and Wastewater, 19th ed.
f) Total Phosphorus by Method 4500-P C, Standard Methods for the Examination of Water and
Wastewater, 19th ed.
g) Conductivity by Method 2510 B, Standard Methods for the Examination of Water and
Wastewater, 19th ed.
h) Nitrate-Nitrogen by US EPA Method 300.0
i) Total Organic Carbon by Hach Method 10173
j) Temperature by lab grade thermometer
Site Sampling Procedure
Prior to departure for each selected sampling site, sample interval and duration parameters for
the sonde were adjusted and set to begin at a predetermined time; typically 8:30 am, and to take
readings at 30 minute intervals for a period of 7 days.
Upon arrival at each site, and once the optimum location for the apparatus was determined, the
water temperature and manual depth were measured, and the frame stakes put into position. The cage
3
was then mounted to the stakes and adjusted to the appropriate depth. In each case, this was 6 inches
from the bed of the stream per IEPA recommendations. During the initial set-up, and in one case,
retrieval of the apparatus, a member of the engineering department took GPS measurements for
mapping purposes, and assistance in estimating flow rates.
Just prior to placing the sonde in the cage, water samples were collected for additional lab
analysis. The sonde was then carefully loaded in the cage (with the probes facing upstream), and the
cage closed and secured with a long-shackle padlock. Additionally, a heavy-duty cable was looped
around a nearby stationary object (usually a tree near the shore), and the other looped end was placed
on the same padlock. Water samples were then taken back to the lab to begin analysis.
During the 7 day sampling period, a member of the lab staff went out on a daily basis, to check
the apparatus for obvious tampering, and to ensure there were no debris hang-ups. At the end of the
sampling period the lab staff returned to the site, and began again, by taking water temperature and
manual depth measurements. Within 5 minutes of the final sampling, interval additional water samples
were again collected for lab analysis. After the final sampling interval, the sonde was removed and taken
to shore so the data could be transferred to the lap-top computer. Data was checked to ensure no
obvious problems, such as fouling of the probes. Once the data was satisfactorily transferred to the laptop computer, all equipment was gathered and taken back to the lab, where analysis of the samples was
begun, equipment cleaned, and the sonde checked for calibration drift.
4
Site One Results:
Site One : Sangamon River at Lincoln Homestead State Park
Geographical location of sonde placement : Latitude: 39o 48’ 3.13" North
Longitude: 89o 6’ 18.3" West
Continuous Monitoring Conditions at start of period:
Samplers: Bill Cunningham, Jeff Runyon, Jared Harris, Larry Arnold
Placement site characteristics: run following upstream riffle at park pull-off, just prior to Sangamon River
Bridge on Lincoln State Memorial Parkway
5
Sampling start time: 08:30 on July 28, 2011 with sampling interval of 30 minutes
Sampling stop time: 08:30 on August 4, 2011
Stream depth placement: 2 feet 2 inches by manual measurement
Sonde depth placement: 1 foot 8 inches by manual measurement
Estimated river flow = 70 ft width x 1.45 ft average depth x ca 1 ft/sec flow = ca 100 cfs
Weather Conditions at start: Cloudy, Humid, 80o F
Sonde Calibration:
Calibration was performed by technical staff at Field Environmental Instruments, Pittsburgh, PA and
results follow:
Instrument 6920
Serial Number 6920R3
Firmware Version 3.10
Calibration Date: 7/13/11
Probe Calibration:
Parameter
Temperature
Sp Conductivity 0 mS/cm
Sp Conductivity 1.413 mS/cm
Dissolved Oxygen % saturation
Chlorophyll 0.0
Chlorophyll 113.0
Result
22.98
0.001
1.413
98.0
0.0
113.0
Pass/Fail
Pass
Pass
Pass
Pass
Pass
Pass
Start of run inaccuracy check:
Parameter
Initial Sonde reading
Dissolved Oxygen, mg/L
6.12
Post run inaccuracy check:
Concurrent Laboratory Result Relative % Difference
5.85
4.5
Parameter
Concurrent Laboratory Result Relative % Difference
5.65
1.4
Dissolved Oxygen, mg/L
Final Sonde reading
5.73
Chlorophyll was considered being performed on a semi-quantitative basis. An Instrument Detection
Limit of 1.0 µg/L was obtained analyzing tap water over a period of time. This translates to a Method
Detection Limit of 4.0 µg/L and a Limit of Quantitation of 10 µg/L.
Criteria established by the Illinois EPA for the inaccuracy check was a relative % difference of less than
20% which was met. (3)
6
7
Calibration Drift:
Parameter
Dissolved Oxygen, mg/L
Test Solution concentration
8.87
Sonde reading
Relative % Difference
8.83
0.45
Criteria established by the Illinois EPA for the calibration drift check was an absolute difference of less
than 0.4 mg/L for DO which was met. (3)
Continuous Monitoring Results for Dissolved Oxygen:
During this run, water temperature ranged from 27.7 to 32.0 degrees C with an average of 29.9.
Chlorophyll ranged from 6.6 to 44 µg/L with an average of 20.
Dissolved Oxygen ranged from 5.73 to 11.5 mg/L with an average of 8.22.
Conductivity ranged from 2.663 to 2.946 mS/cm with an average of 2.801.
8
Daily Dissolved Oxygen Summary
(Each 24 hour period started at 8:30 a.m. and the final reading taken at 8:00 a.m. the next day)
Average
Minimum
Maximum
D.O. Swing
Period Start Date
D.O. (mg/L)
D.O. (mg/L) D.O. (mg/L)
(mg/L)
7/28/11
8.52
6.12
11.17
5.05
7/29/11
8.36
6.53
10.73
4.20
7/30/11
8.27
6.49
10.44
3.95
7/31/11
8.52
6.30
11.24
4.94
8/01/11
8.45
5.88
11.54
5.66
8/02/11
7.86
5.85
10.65
4.80
8/03/11
7.57
5.73
10.00
4.27
Since the lowest water temperature occurring during this run was ca 28 degrees centigrade and the
elevation of the area is around 570 feet above sea level, the solubility of oxygen in fresh water at that
temperature would be around 7.7 mg/L (4). Therefore, super saturation was occurring during the
photosynthetic periods of the day.
Water Quality Results for Site One at sample start up and completion :
Parameter
Day One (7/28)
Day Seven (8/4)
Total Suspended Solids (mg/L)
27
26
Total Organic Carbon (mg/L)
6
7
Ammonia-Nitrogen (mg/L)
0.07
0.06
Nitrate-Nitrogen (mg/L)
15.2
15.6
Phosphate-Phosphorus (mg/L), total
9.48
11.6
pH, S.U.
7.85
7.85
Specific Conductance, mS/cm
2.34
2.70
Dissolved Oxygen, mg/L
5.85
5.65
Hardness, mg/L
348
372
Nickel (mg/L), Total
0.0140
0.0159
Zinc (mg/L), Total
0.0168
0.0176
Weather Conditions for Site One Monitoring
Date
7/28/11
7/29/11
7/30/11
7/31/11
8/1/11
8/2/11
8/3/11
8/4/11
Maximum Temperature, o F
96
89
87
93
94
96
93
89
Minimum Temperature, o F
77
74
70
71
69
78
68
63
Precipitation, “
0
T
0
0
0
0
0
0
9
Site Two Results :
Site Two: Sangamon River at Rock Springs Center just upstream from Wyckle’s Road Bridge
Geographical location of sonde placement: Latitude: 39o 48’ 03.137 " North
Longitude: 89o06’ 18.325" West
Continuous Monitoring Conditions at start of period:
Samplers: Bill Cunningham, Jeff Runyon, Jared Harris, Larry Arnold, Lee Slider
Placement site characteristics: run just upstream from Wyckle’s Road Bridge
Sampling start time: 08:30 on August 11, 2011 with sampling interval of 30 minutes
Sampling stop time: 08:30 on August 18, 2011
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Stream depth placement: 2 feet 2 1/2 inches by manual measurement
Sonde depth placement: 1 foot 8 1/2 inches by manual measurement
Estimated river flow = 106 ft width x 2.1 ft average depth x ca 0.25 ft/sec flow = ca 56 cfs
Weather Conditions at start: Sunny, Dry, 67o F
Sonde Calibration:
Calibration was performed by Sanitary District staff and results follow:
Instrument 6920
Serial Number 6920R3
Firmware Version 3.10
Calibration Date: 8/10/11
Probe Calibration:
Parameter
Dissolved Oxygen mg/L
Result
8.85 @ 20.0 o C
Action
Set to Winkler result
obtained for air-saturated water
Start of run inaccuracy check:
Parameter
Dissolved Oxygen, mg/L
Initial Sonde reading
5.27
Concurrent Laboratory Result Relative % Difference
5.16
2.11
Post run inaccuracy check:
Parameter
Dissolved Oxygen, mg/L
Final Sonde reading
4.47
Concurrent Laboratory Result Relative % Difference
5.00
11.2
Chlorophyll was considered being performed on a semi-quantitative basis.
Criteria established by the Illinois EPA for the inaccuracy check was a relative % difference of less than
20% which was met for the parameter evaluated. (3)
Calibration Drift:
Parameter
Dissolved Oxygen, mg/L
Test Solution concentration
8.35
Sonde reading
Relative % Difference
8.20
1.81
Criteria established by the Illinois EPA for the calibration drift check was an absolute difference of less
than 0.4 mg/L for DO which was met. (3)
11
12
Continuous Monitoring Results for Dissolved Oxygen:
During this run, water temperature ranged from 25.6 to 30.3 degrees C with an average of 27.9.
Chlorophyll ranged from 3.8 to 108 µg/L with an average of 9.2.
Dissolved Oxygen ranged from 4.25 to 8.41 mg/L with an average of 6.19.
Conductivity ranged from 3.297 to 3.596 mS/cm with an average of 3.442.
Daily Dissolved Oxygen Summary
(Each 24 hour period started at 8:30 a.m. and the final reading taken at 8:00 a.m. the next day)
Average
Minimum
Maximum
D.O. Swing
Period Start Date
D.O. (mg/L)
D.O. (mg/L) D.O. (mg/L)
(mg/L)
8/11/11
6.27
5.08
8.00
2.92
8/12/11
6.25
5.03
8.12
3.09
8/13/11
6.03
4.82
7.81
2.99
8/14/11
6.15
4.95
8.10
3.15
8/15/11
6.26
4.98
8.41
3.43
8/16/11
6.23
4.87
8.36
3.49
8/17/11
6.13
4.25
8.21
3.96
13
Since the lowest water temperature occurring during this run was ca 26 degrees centigrade and the
elevation of the area is 580 feet above sea level, the solubility of oxygen in fresh water at that
temperature would be around 8.0 mg/L (4). Therefore, some slight super saturation appears to have
occurred during the photosynthetic periods of the day.
Water Quality Results for Site Two at sample start up and completion:
Parameter
Day One (8/11)
Total Suspended Solids (mg/L)
7.0
Total Organic Carbon (mg/L)
13
Ammonia-Nitrogen (mg/L)
0.20
Nitrate-Nitrogen (mg/L)
19.0
Phosphate-Phosphorus (mg/L), total
13.7
pH, S.U.
8.04
Specific Conductance, mS/cm
2.98
Dissolved Oxygen, mg/L
5.16
Hardness, mg/L
367
Nickel (mg/L), Total
0.0200
Zinc (mg/L), Total
0.0277
Day Seven (8/18)
7.5
16
0.17
13.1
15.6
8.00
3.16
5.00
373
0.0208
0.0186
Weather Conditions for Site Two Monitoring
Date
8/11/11
8/12/11
8/13/11
8/14/11
8/15/11
8/16/11
8/17/11
8/18/11
Maximum Temperature, o F
83
86
89
83
84
84
87
91
Minimum Temperature, o F
55
56
64
61
56
54
59
66
Precipitation, “
0
T
T
0
0
0
0
0
14
Site Three Results:
Site Three: Sangamon River at 7th Ward Combined Sewer Overflow (upstream from treatment plant)
Geographical location of sonde placement: Not Determined due to sonde enclosure being pulled form
water between 5:30 pm and 6:00 pm, August 27. Since this point was not critical to this evaluation, it
was decided to abort this site due to the vandalism potential. Partial results are presented below.
Continuous Monitoring Conditions at start of period:
Samplers: Bill Cunningham, Jeff Runyon, Larry Arnold
Placement site characteristics: pool just upstream from CSO discharge point
Sampling start time: 08:30 on August 25, 2011 with sampling interval of 30 minutes
Sampling stop time: 09:30 on August 29, 2011 – last valid in water reading at 17:30 on August 27, 2011
Stream depth placement: 2 feet 7 inches by manual measurement
Sonde depth placement: 2 foot 1 inches by manual measurement
Estimated river flow = ca 0 cfs (no dam discharge occurring and no observable flow)
Weather Conditions at start: Sunny, Dry, 60o F
Because the engineering technician was not available on start up day, no gps readings were taken. The
intent was to do them at completion time. However, this was not done due to the sonde being pulled
out of the water prematurely.
Instrument 6920
Serial Number 6920R3
Firmware Version 3.10
Calibration Date: 8/23/11
Probe Calibration:
Parameter
Dissolved Oxygen mg/L
Result
8.95 @ 20.0 o C
Start of run inaccuracy check:
Parameter
Initial Sonde reading
Dissolved Oxygen, mg/L
3.52
Action
Set to Winkler result
obtained for air-saturated water
Concurrent Laboratory Result Relative % Difference
4.10
15.2
15
Chlorophyll was considered being performed on a semi-quantitative basis.
Criteria established by the Illinois EPA for the inaccuracy check was a relative % difference of less than
20% which was met for the parameter evaluated. (3)
During this aborted run, water temperature ranged from 23.2 to 26.3 degrees C with an average of 24.7.
Chlorophyll ranged from 11 to 28 µg/L with an average of 19.
Dissolved Oxygen ranged from 2.60 to 6.45 mg/L with an average of 4.35.
Conductivity ranged from 0.643 to 0.679 mS/cm with an average of 0.658.
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Daily Dissolved Oxygen Summary
(Each 24 hour period started at 8:30 a.m. and the final reading taken at 8:00 a.m. the next day)
Average
Minimum
Maximum
D.O. Swing
Period Start Date
D.O. (mg/L)
D.O. (mg/L) D.O. (mg/L)
(mg/L)
8/25/11
4.46
2.69
6.45
3.76
8/26/11
4.38
2.60
6.32
3.72
8/27/11
4.00
2.69
5.20
2.51
(8/27/11 data represents 9 hours monitoring before device was pulled from river)
No super saturation occurred at this site.
Water Quality Results for Site Three at sample start up and completion:
Parameter
Day One (8/25)
Total Suspended Solids (mg/L)
26.5
Total Organic Carbon (mg/L)
8
Ammonia-Nitrogen (mg/L)
0.11
Nitrate-Nitrogen (mg/L)
0.242
Phosphate-Phosphorus (mg/L), total
5.90
pH, S.U.
7.91
Specific Conductance, mS/cm
6.41
Dissolved Oxygen, mg/L
4.10
Hardness, mg/L
331
Nickel (mg/L), Total
0.00286
Zinc (mg/L), Total
0.0141
Weather Conditions for Site Three Monitoring
Date
8/25/11
8/26/11
8/27/11
Maximum Temperature, o F
87
88
90
Minimum Temperature, o F
63
57
63
Precipitation, “
0
0
0
17
Site Two (Run 2) Results (corresponds to engineering site 3 on gps diagram) :
Site Two, Run 2: Sangamon River at Rock Springs Center just upstream from Wyckle’s Road Bridge
Geographical location of sonde placement: Latitude: 39o 49’ 27.652 " North
Longitude: 89o01’ 40.208" West
Continuous Monitoring Conditions at start of period:
Samplers: Bill Cunningham, Jeff Runyon, and Larry Arnold
Placement site characteristics: run just upstream from Wyckle’s Road Bridge
Sampling start time: 08:30 on September 1, 2011 with sampling interval of 30 minutes
Sampling stop time: 08:30 on September 8, 2011
Stream depth placement: 2 feet 8 inches by manual measurement
Sonde depth placement: 2 foot 2 inches by manual measurement
Estimated river flow = 109 ft width x 2.0 ft average depth x ca 0.25 ft/sec flow = ca 55 cfs
Weather Conditions at start: Sunny, Dry, 80 o F
Instrument 6920
Serial Number 6920R3
Firmware Version 3.10
Calibration Date: 8/23/11
Probe Calibration:
Parameter
Dissolved Oxygen mg/L
Result
8.93 @ 20.0 o C
Action
Set to Winkler result
obtained for air-saturated water
Start of run inaccuracy check:
Parameter
Dissolved Oxygen, mg/L
Initial Sonde reading
4.98
Concurrent Laboratory Result Relative % Difference
4.87
2.23
Post run inaccuracy check:
Parameter
Dissolved Oxygen, mg/L
Final Sonde reading
4.92
Concurrent Laboratory Result Relative % Difference
5.38
8.93
18
Chlorophyll was considered being performed on a semi-quantitative basis.
Criteria established by the Illinois EPA for the inaccuracy check was a relative % difference of less than
20% which was met for the parameter evaluated. (3)
Calibration Drift:
Parameter
Dissolved Oxygen, mg/L
Test Solution concentration
8.93
Sonde reading
Relative % Difference
9.03
1.11
Chlorophyll was considered being performed on a semi-quantitative basis.
Criteria established by the Illinois EPA for the inaccuracy check was a relative % difference of less than
20% which was met for the parameter evaluated. (3)
During this run, water temperature ranged from 22.9 to 31.7 degrees C with an average of 27.2.
Chlorophyll ranged from 4.0 to 171.5 µg/L with an average of 16.2.
Dissolved Oxygen ranged from 4.44 to 9.06 mg/L with an average of 5.95.
Conductivity ranged from 2.784 to 3.718 mS/cm with an average of 3.282.
19
20
Daily Dissolved Oxygen Summary
(Each 24 hour period started at 8:30 a.m. and the final reading taken at 8:00 a.m. the next day)
Average
Minimum
Maximum
D.O. Swing
Period Start Date
D.O. (mg/L)
D.O. (mg/L) D.O. (mg/L)
(mg/L)
9/01/11
6.39
4.58
9.06
4.48
9/02/11
6.18
4.49
8.84
4.35
9/03/11
6.08
4.65
8.77
4.12
9/04/11
5.28
4.44
6.46
2.02
9/05/11
5.61
4.51
7.42
2.91
9/06/11
5.92
4.60
7.86
3.26
9/07/11
6.19
4.83
8.18
3.35
Since the lowest water temperature occurring during this run was ca 23 degrees centigrade and the
elevation of the area is 580 feet above sea level, the solubility of oxygen in fresh water at that
temperature would be around 8.4 mg/L (4). Therefore, some slight super saturation appears to have
occurred during the photosynthetic periods of the day.
Parameter
Total Suspended Solids (mg/L)
Total Organic Carbon (mg/L)
Ammonia-Nitrogen (mg/L)
Nitrate-Nitrogen (mg/L)
Phosphate-Phosphorus (mg/L), total
pH, S.U.
Specific Conductance, mS/cm
Dissolved Oxygen, mg/L
Hardness, mg/L
Nickel (mg/L), Total
Zinc (mg/L), Total
Day One (9/01)
13
17
0.24
17.4
16.9
8.11
3.230
4.87
369
0.0197
0.0197
Day Seven (9/08)
14
23
0.20
20.9
18.5
7.91
3.220
5.38
362
0.0194
0.0256
Weather Conditions for Site Two Run 2 Monitoring
Date
Maximum Temperature, o F Minimum Temperature, o F
9/01/11
100
76
9/02/11
101
71
9/03/11
98
67
9/04/11
79
62
9/05/11
73
52
9/06/11
73
47
9/07/11
76
50
9/08/11
78
52
Precipitation, “
0
0
0.41
0
0
0
0
0.11
21
RESULTS DISCUSSION
As written by Dr. JoAnn Burkholder who represents the Mississippi River Collaborative: “Some
Illinois EPA personnel have suggested that as an evaluation method, Illinois waters could be considered
to require protection from nutrient pollution only if they met all three of the following characteristics: #1)
wide variation in dissolved oxygen (DO) concentrations (> 6 mg DO/L, referred to as DO “swings.”) over a
diel (24-hour) cycle; #2) super saturation during the sunny part of the day, when algal photosynthesis
would be expected to be highest; and #3) DO levels in early morning less than the standard to protect
beneficial aquatic life (generally 5 mg/L); this condition is referred to as having a pre-dawn DO
“sag.””(2).
The specific Illinois water quality standard for Dissolved Oxygen as applies to the Sangamon
River at the Sanitary District of Decatur discharge point is as follows:
“Section 302.206
Dissolved Oxygen
General use waters must maintain dissolved oxygen concentrations at or above the values contained in
subsections (a), (b) and (c) of this Section.
a)
General use waters at all locations must maintain sufficient dissolved oxygen
concentrations to prevent offensive conditions as required in Section 302.203 of
this Part. Quiescent and isolated sectors of General Use waters including but not
limited to wetlands, sloughs, backwaters and waters below the thermocline in
lakes and reservoirs must be maintained at sufficient dissolved oxygen
concentrations to support their natural ecological functions and resident aquatic
communities.
b)
Except in those waters identified in Appendix D of this Part, the dissolved oxygen
concentration in the main body of all streams, in the water above the
thermocline of thermally stratified lakes and reservoirs, and in the entire water
column of unstratified lakes and reservoirs must not be less than the following:
1)
2)
During the period of March through July,
A)
5.0 mg/L at any time; and
B)
6.0 mg/L as a daily mean averaged over 7 days.
During the period of August through February,
A)
3.5 mg/L at any time;
B)
4.0 mg/L as a daily minimum averaged over 7 days; and
C)
5.5 mg/L as a daily mean averaged over 30 days. (5)”
An evaluation of each site as related to the three criteria mentioned above using the
actual Illinois D.O. water quality standard follows:
22
Site One (Lincoln Homestead Park downstream from district discharge):
1) D.O. swings were < 6 mg/L – criteria does not apply
2) Super saturation was occurring – criteria does apply
3) All D.O.’s > 5.73 mg/L and Average 7 day D.O. is 8.22 mg/L - criteria does not apply
Site Two Run 1 (Rock Springs Center near Wyckle’s bridge downstream from district discharge):
1) D.O. swings were < 6 mg/L – criteria does not apply
2) Super saturation was occurring – criteria does apply
3) All D.O.’s >= 4.25 mg/L - criteria does not apply
Site Two Run 2 (Rock Springs Center near Wyckle’s bridge downstream from district discharge):
1) D.O. swings were < 6 mg/L – criteria does not apply
2) Super saturation was occurring – criteria does apply
3) All D.O.’s >= 4.44 mg/L - criteria does not apply
At the upstream site near 7th Ward CSO facility (during the abbreviated run), D.O. readings were
obtained below the 3.5 mg/L at any time criteria, but of course, no 7 day determination can be
made with the incomplete data set obtained.
One of our criteria for this study was to perform the evaluation during a “worst case scenario”
of low flow in the Sangamon River. During the study period of July 28, 2011 through September 8, 2011,
the river flow upstream from the district discharge ranged from 0.15 to 4.1 cubic feet/second with a
mean of 1.8. Plant effluent flows were at summer lows during most of this period and were generally
between 20 and 30 million gallons per day. Rainfall during the period was minimal and cloudy days were
the exception during the period.
(1) NPDES Permit No. IL0028321 for Sanitary District of Decatur Main STP, Effective Date : July 1,
2007, Illinois EPA, Issue date : April 20,2007.
(2) Comments on Potential Use of Diel Patterns in Dissolved Oxygen Concentrations to Assess
Nutrient Impairment in Illinois Surface waters, Dr. JoAnn Burkholder, April 29, 2011.
(3) Standard Operating Procedure for Continuous Monitoring of Water Quality, Illinois EPA, Bureau
of Water Document Control Number 128, Version 1.4, May 2010.
(4) Making Dissolved Oxygen Measurements, YSI Incorporated.
(5) Environmental Regulations for the State of Illinois, Title 35 of the Illinois Administrative Code,
Subtitle A: General Provisions, Subtitle C: Water Pollution, Chapter I: Pollution Control Board,
Part 302: Water Quality Standards,
http://www.ipcb.state.il.us/SLR/IPCBandIEPAEnvironmentalRegulations-Title35.asp