Assessment Summary
The Class A1 use was assessed as "not supported" based on levels of indicator bacteria (E. coli) that violated state water quality criteria. The Class BWW1 use was assessed as "WINOFI" based on the occurrence of a single fish kill. The Class C use was assessed as "fully supported" based on water quality monitoring data and drinking water compliance monitoring required by the DNR. The Class HH use was assessed as "fully supported" based on fish tissue sampling data.
A TMDL for bacteria was prepared by DNR and approved by U.S. EPA in March 2010. Because this TMDL covers the bacteria impairment identified for this segment, the Class A1 designated use remain in IR Category 4a (impaired; TMDL approved) for this cycle. Additionally, a TMDL for nitrate was prepared by DNR and approved by EPA in September 2009. However, the 2022-2024 nitrate monitoring data indicated "full support."
Assessment Explanation
Data Sources:
|
Data
Source
|
Data
Source ID
|
Data Type
|
Data Age
|
Site ID
|
Site Name
|
Site Description
|
|
DMWW
|
13
|
WQ
|
CY
2022-2024
|
99990015
|
Des Moines River
|
|
|
USACE
|
12
|
FT
|
See Below
|
17770001
|
Des Moines River at
66th. St.
|
Site 5
|
Class A1 - Indicator Bacteria:
|
Site ID
|
Data
Source ID
|
# Samples
per Year (2022/ 2023/2024)
|
2022
Geometric Mean
|
2023
Geometric Mean
|
2024
Geometric Mean
|
Violates
Annual Geometric Mean?
|
# 2022
SSM violations / SSM Violations needed for impairment
|
# 2023
SSM violations / SSM Violations needed for impairment
|
# 2024
SSM violations / SSM Violations needed for impairment
|
Violates
Annual SSM Significantly >10% Rule?
|
Assessment
Type
|
Support
Level
|
|
99990015
|
13
|
170/170/158
|
39
|
38
|
38
|
NO
|
18 / 23
|
21 / 23
|
26 / 22
|
YES
|
MONITORED
|
NOT
|
Class A1 - pH:
|
Site ID
|
Data
Source ID
|
# Samples
/ # Years
|
Minimum
Value
|
Maximum
Value
|
Mean
Value
|
#
Violations
|
Violations
needed for impairment
|
Violates
Significantly >10% Rule?
|
Assessment
Type
|
Support
Level
|
|
99990015
|
13
|
759 / 3
|
7.63
|
8.96
|
8.27
|
0
|
88
|
NO
|
MONITORED
|
FULL
|
Class BWW1 - Binomial Parameters:
|
Site ID
|
Data
Source ID
|
Parameter
Name
|
# Samples
/ # Years
|
Minimum
Value
|
Maximum
Value
|
Mean
Value
|
#
Violations
|
# Acute /
Chronic Violations
|
Violations
needed for impairment
|
Violates
Significantly >10% Rule?
|
Assessment
Type
|
Support
Level
|
|
99990015
|
13
|
Chloride
|
759 / 3
|
13.69
|
100.01
|
38.54
|
NA
|
0 / 0
|
88
|
NO
|
MONITORED
|
FULL
|
|
99990015
|
13
|
pH
|
759 / 3
|
7.63
|
8.96
|
8.27
|
0
|
NA / NA
|
88
|
NO
|
MONITORED
|
FULL
|
|
99990015
|
13
|
Sulfate
|
759 / 3
|
21.63
|
147.51
|
82.75
|
0
|
NA / NA
|
88
|
NO
|
MONITORED
|
FULL
|
|
99990015
|
13
|
Temperature
|
758 / 3
|
-1.11
|
29.44
|
12.94
|
0
|
NA / NA
|
87
|
NO
|
MONITORED
|
FULL
|
Class BWW1 - Toxic Parameters:
|
Site ID
|
Data
Source ID
|
Parameter
Name
|
# Samples
/ # Years
|
Maximum
Value
|
Mean
Value
|
Median
Value
|
# Acute /
Chronic Violations
|
>1
Acute / Chronic Violation
|
Assessment
Type
|
Support
Level
|
|
99990015
|
13
|
Ammonia
|
757 / 3
|
1.06
|
0.11
|
0.05
|
0 / 0
|
NO
|
MONITORED
|
FULL
|
|
99990015
|
13
|
Lead
|
72 / 3
|
2.5
|
2.5
|
2.5
|
0 / 0
|
NO
|
MONITORED
|
FULL
|
Class C - Binomial Parameters:
|
Site ID
|
Data
Source ID
|
Parameter
Name
|
# Samples
/ # Years
|
Minimum
Value
|
Maximum
Value
|
Mean
Value
|
Median
Value
|
#
Violations
|
Violates
Significantly >10% Rule?
|
Assessment
Type
|
Support
Level
|
|
99990015
|
13
|
Chloride
|
759 / 3
|
13.69
|
100.01
|
38.54
|
37.09
|
0
|
NO
|
MONITORED
|
FULL
|
|
99990015
|
13
|
Fluoride
|
758 / 3
|
200
|
560
|
388
|
390
|
0
|
NO
|
MONITORED
|
FULL
|
|
99990015
|
13
|
Nitrate
|
759 / 3
|
0.05
|
15.56
|
3.3
|
1.79
|
52
|
NO
|
MONITORED
|
FULL
|
|
99990015
|
13
|
Nitrite
|
759 / 3
|
0.05
|
0.39
|
0.07
|
0.05
|
0
|
NO
|
MONITORED
|
FULL
|
|
99990015
|
13
|
pH
|
759 / 3
|
7.63
|
8.96
|
8.27
|
8.27
|
0
|
NO
|
MONITORED
|
FULL
|
Class BWW1 - Fish kill Assessment:
A July 2024 fish kill occurred in the Des Moines River immediately downriver from the Saylorville dam that was caused by gas bubble trauma (GBT). Fish kills caused by GBT occur due to a large imbalance between the concentrations of atmospheric gasses in the water and the levels of these gasses dissolved in the blood of the fish. The concentrations of dissolved gasses such as oxygen and nitrogen in river water tend to equal the concentrations in the blood of a fish. When the levels of atmospheric gasses dissolved in river water become very high (i.e., super-saturated)—such as can happen when water moves through or over a large dam—the levels of these gasses will also rise in the blood of fish. As long as fish can stay in deeper water, the hydrostatic (water) pressure will keep these gasses fully dissolved in the fish’s blood. If, however, the flow of water downstream from the dam is decreased suddenly, the depth of the water will also decrease. With shallower water, fish are not able to move to deeper areas to keep the hydrostatic pressure sufficiently high to keep the gasses fully dissolved in their blood. During these conditions, the gasses dissolved in the fish’s blood will gradually come out of solution as bubbles, and these bubbles will interfere with blood circulation. Symptoms of gas bubble trauma in fish include gas blisters on the skin at the margins of the scales and as pop-eye (exophthalmia) where the eyes of the fish distend from the eye sockets. In the extreme case, blood circulation is disrupted to the point that fish kills occur.
The aquatic life use was placed in Category 3b (WINOFI list – potential impairment) because there weren’t multiple fish kills in this segment in the last five years. Should additional GBT fish kills occur in this segment in the future, the aquatic life use will be moved to IR Category 5b and be placed on the Impaired Waters List.
Details about the 2024 fish kill can be found here:https://programs.iowadnr.gov/fishkill/events/1059
Class C - Iowa Drinking Water Compliance Report:
Compliance monitoring required by the Iowa DNR Water Supply
Operations and Engineering Sections did not show violations of finished water
caused by source water at the Des Moines Water Works facility during the 2022-2024
monitoring period. The results of compliance monitoring as reported in annual
compliance reports are available at the following location at the Iowa DNR’s
home page: https://www.iowadnr.gov/Environmental-Protection/Water-Quality/Water-Supply-Engineering/Annual-Compliance-Report.
Class HH - Fish Tissue
Sampling:
|
Site ID
|
Biopart
|
Year
|
Species
|
# in sample / # of
samples
|
Avg Length (cm)
|
(Avg) Hg (ppm)
|
Chlordane (ppm)
|
Sum PCBs (ppm)
|
|
17770001
|
whole
|
2016
|
common carp
|
5
|
NA
|
NA
|
0.03
|
<0.06
|
|
17770001
|
fillet
|
2016
|
largemouth bass
|
2
|
NA
|
0.11
|
|
|
|
Support Level
|
Full
|
Monitored
|
|
|
|
|
|
|
