2024 Pending assessment for West Fork Little Sioux River

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

For purposes of developing stream/river water quality assessments for integrated reporting, three years of water quality data are typically used for both conventional pollutant parameters (e.g., indicator bacteria) and the less frequently monitored toxic parameters (e.g., toxic metals). Since the 2004 IR cycle, DNR has used a three-year data gathering period for streams, rivers, and beaches. For most assessments, the use of three years of data increases the number of samples upon which the decision on use support is based and helps address the problem of weather-related year-to-year fluctuations in water quality.

Due to the lower sampling frequency in Iowa’s ambient lake, biological, fish kill, and fish tissue monitoring programs, five years of data are used for developing IR assessments and for identifying Section 303(d) listings.

Data Type	Data Timeframe
Beach Sampling Data	CY 2020 - 2022
Stream/River Water Quality Data	CY 2020 - 2022
Lake Water Quality Data	CY 2018 - 2022
Biological Sampling Data	CY 2018 - 2022*
Fish Kill Data	CY 2018 - 2022
Fish Tissue Sampling Data	CY 2018 - 2022
Continuous Dissolved Oxygen Sampling Data	CY 2018 - 2022
*Biological sites sampled in both 2017 and 2021 were also assessed.

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

Not Supported

Bacteria: Indicator Bacteria- E. coli

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

Not Supported

Metals: Selenium

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

Biological: low aquatic macroinvertebrate IBI

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

8/8/8

227

192

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

Water Quality Assessments

Impaired Waters List

West Fork Little Sioux River IA 06-LSR-1598

Assessment Summary

Assessment Explanation

Assessment Key Dates

Methods