Iowa DNR
Iowa DNR
ADBNet
Water Quality Assessments
Impaired Waters List

West Fork Little Sioux River IA 06-LSR-1598

mouth (S12 T84N R45W Monona Co.) to confluence with a small unnamed tributary near Climbing Hill in S16 T87N R45W Woodbury Co.

Assessment Cycle
2024
Release Status
Pending
Data Collection Period
Overall IR Category
5 - Water is impaired or threatened and a TMDL is needed.
Trend
Stable
Created
11/1/2023 8:13:04 AM
Updated
2/1/2024 6:56:21 AM
Assessment conducted in accordance with Iowa's 2024 IR methodology.
Use Support
Class A1
Recreation
Primary contact
Not Supported
Impairments
Support Level
Not Supported
Impairment Code
5a - Pollutant-caused impairment. TMDL needed.
Cause Magnitude
Slight
Status
Continuing
Source
Unknown: Source Unknown
Source Confidence
Low
Cycle Added
2008
Impairment Rationale
Geometric mean criterion exceeded
Data Source
Ambient monitoring: Iowa DNR-rivers
TMDL Priority
Tier III
Class BWW2
Aquatic Life
Warm Water Type 2
Not Supported
Impairments
Support Level
Not Supported
Impairment Code
5a - Pollutant-caused impairment. TMDL needed.
Cause Magnitude
Slight
Status
Continuing
Source
Unknown: Source Unknown
Source Confidence
N/A
Cycle Added
2022
Impairment Rationale
Violations of chronic criterion
Data Source
Ambient monitoring: Iowa DNR-rivers
TMDL Priority
Tier III
Support Level
Water in Need of Further Investigation (WINOFI)
Impairment Code
3b-c - Use potentially biologically impaired based on calibrated IBI metrics.
Cause Magnitude
Moderate
Status
New
Source
Unknown: Source Unknown
Source Confidence
Low
Cycle Added
2024
Impairment Rationale
Potential Impairment
Data Source
Biological monitoring: Iowa DNR WQMA
Impairment Delistings
No delistings for this assessment cycle.
Documentation
Assessment Summary

The Class A1 use was assessed as "not supported" due to levels of indicator bacteria (E. coli) that violated state water quality criteria. The Class BWW2 use was assessed as "not supported" based on violations of the state water quality chronic criteria for selenium and "WINOFI" based on biological sampling data.

Assessment Explanation

Data Sources:

Data Source

Data Source ID

Data Type

Data Age

Site ID

Site Name

Site Description

Iowa DNR

6

WQ

CY 2020-2022

10970002

West Fork Ditch at Hornick

Iowa DNR

6

BIO

See Below

934

West Fork Little Sioux River

Hornick


Class A1 - Indicator Bacteria:

Site ID

Data Source ID

# Samples per Year (2020/ 2021/2022)

2020 Geometric Mean

2021 Geometric Mean

2022 Geometric Mean

Violates Annual Geometric Mean?

# 2020 SSM violations / SSM Violations needed for impairment

# 2021 SSM violations / SSM Violations needed for impairment

# 2022 SSM violations / SSM Violations needed for impairment

Violates Annual SSM Significantly >10% Rule?

Assessment Type

Support Level

10970002

6

8/8/8

227

192

95

YES

3 / 3

5 / 3

2 / 3

YES

Mon

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

10970002

6

36 / 3

7.4

8.6

8.1

0

7

NO

Mon

Full


Class BWW2 - 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

10970002

6

Chloride

36 / 3

16

36

19

NA

0 / 0

7

NO

Mon

Full

10970002

6

Dissolved Oxygen

36 / 3

7.6

15.9

10.9

0

NA / NA

7

NO

Mon

Full

10970002

6

pH

36 / 3

7.4

8.6

8.1

0

NA / NA

7

NO

Mon

Full

10970002

6

Sulfate

36 / 3

51

120

78

0

NA / NA

7

NO

Mon

Full

10970002

6

Temperature

36 / 3

0

27.1

12.4

0

NA / NA

7

NO

Mon

Full


Class BWW2 - 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

10970002

6

Ammonia

36 / 3

0.73

0.05

0.02

0 / 0

NO

Mon

Full

10970002

6

Cadmium

20 / 3

0.5

0.5

0.5

0 / 0

NO

Mon

Full

10970002

6

Chromium

20 / 3

2

0.82

0.7

0 / 0

NO

Mon

Full

10970002

6

Lead

20 / 3

1

0.93

1

0 / 0

NO

Mon

Full

10970002

6

Nickel

20 / 3

3.1

1.7

1.4

0 / 0

NO

Mon

Full

10970002

6

Selenium

18 / 2

8

6

6

0 / 9

YES

Mon

Not

10970002

6

Silver

20 / 3

1

0.902

1

0 / 0

NO

Mon

Full

10970002

6

Zinc

20 / 3

3.3

0.9

0.5

0 / 0

NO

Mon

Full


Class BWW2 - Biological Sampling:


Benthic Macroinvertebrates:

Site ID

Date

Drainage Area (mi2)

Ecoregion

Major Drainage

BM Sample Gear

BMIBI score

BMIBI Class

47a BMIBI BIT

BMIBI Pass/Fail

934

8/13/19

399

47d

MO

Floating Art Sub

40

Fair

54

Fail


Overall:

Community

Assessment Type

Assessment Result

Support Level

IR Category

Reason

Benthic Macroinvertebrates

Evaluated

Fail (0/1)

WINOFI

Overall

Evaluated

Fail

WINOFI

3bc

Assessment was evaluated because it was based on a single sample.



Monitoring and Methods
Assessment Key Dates
1/7/2020
Monitoring Start
12/13/2022
Monitoring End
8/13/2019
Biological Monitoring
Methods
200
Physical/Chemical Monitoring
315
Regional reference site approach
320
Benthic macroinvertebrate surveys
420
Indicator bacteria monitoring