2024 Pending assessment for Shell Rock River

Shell Rock River IA 02-SHL-783

from south corporate limit of Shell Rock (S12 T91N R15W Butler Co.) to confluence with Flood Cr. in S27 T93N R16W Butler 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: Unknown

Created: 11/1/2023 8:12:48 AM
Updated: 1/17/2024 8:09:56 AM

Assessment conducted in accordance with Iowa's 2024 IR methodology.

Use Support

Class A1

Presumptive Use

Not Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

5p - Impairment occurs on a waterbody with a presumptive A1 or B(WW1) use.

Cause Magnitude

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2018

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Ambient monitoring: Iowa DNR-rivers

TMDL Priority

Tier III

Class BWW1

Fully Supported

Class HH

Not Supported

Fish Consumption Advisory: Mercury

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2012

Impairment Rationale

Fish consumption advisory in effect: no more than 1 meal/week

Data Source

Fish contaminant monitoring: Iowa DNR

TMDL Priority

Tier IV

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The 2020-2022 E. coli data suggest full support of the Class A1 use; however, delisting an impairment requires a monitored assessment. Therefore, the Category 5p Class A1 impairment will remain. The Class BWW1 use was assessed as "fully supported" based on biological sampling data and water quality monitoring data. The Class HH use remains assessed as "not supported" based on fish tissue sampling data and due to a historic one meal/week mercury consumption advisory for any predator fish in this segment.

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	10120001	Shell Rock River at Shell Rock
Iowa DNR	6	BIO	See Below	843	Shell Rock River	Shell Rock
Iowa DNR	6	BIO	See Below	1319	Shell Rock River	Clarksville (REMAP #272)
Iowa DNR	6	FT	See Below	1068	Shell Rock River	W of Clarksville

Presumptive 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

10120001

8/8/8

1 / 3

0 / 3

1 / 3

Eval

Full

The 2020-2022 E. coli data suggest full support of the Class A1 use; however, delisting an impairment requires a monitored assessment. Therefore, the Category 5p Class A1 impairment will remain.

Presumptive 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
10120001	6	36 / 3	7.9	8.7	8.3	0	7	NO	Mon	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
10120001	6	Chloride	36 / 3	10	35	23	NA	0 / 0	7	NO	Mon	Full
10120001	6	Dissolved Oxygen	36 / 3	6.2	14.9	11.2	0	NA / NA	7	NO	Mon	Full
10120001	6	pH	36 / 3	7.9	8.7	8.3	0	NA / NA	7	NO	Mon	Full
10120001	6	Sulfate	36 / 3	14	52	36	0	NA / NA	7	NO	Mon	Full
10120001	6	Temperature	36 / 3	0.2	25.7	11.6	0	NA / NA	7	NO	Mon	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
10120001	6	Ammonia	36 / 3	0.23	0.04	0.02	0 / 0	NO	Mon	Full
10120001	6	Cadmium	20 / 3	0.5	0.5	0.5	0 / 0	NO	Mon	Full
10120001	6	Chromium	20 / 3	2	0.61	0.5	0 / 0	NO	Mon	Full
10120001	6	Lead	20 / 3	1	0.91	1	0 / 0	NO	Mon	Full
10120001	6	Nickel	20 / 3	4.2	1.4	1.1	0 / 0	NO	Mon	Full
10120001	6	Selenium	18 / 2	2	0.8	1	0 / 0	NO	Mon	Full
10120001	6	Silver	20 / 3	1	0.902	1	0 / 0	NO	Mon	Full
10120001	6	Zinc	20 / 3	2.2	0.9	0.5	0 / 0	NO	Mon	Full

Class BWW1 - Biological Sampling:

Benthic Macroinvertebrates:

Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage	BM Sample Gear	BMIBI score	BMIBI Class	47c BMIBI BIT	BMIBI Pass/Fail
843	8/15/22	1730.2	47c	MS	Hess	82	Excellent	70	Pass
1319	9/21/21	1630.0	47c	MS	Hess	63	Good	70	Fail
843	8/23/19	1730.2	47c	MS	Hess	72	Good	70	Pass
843	8/20/19	1730.2	47c	MS	Hess	58	Good	70	Fail
843	8/15/16	1730	47c	MS	Hess	81	Excellent	70	Pass

Fish:

BioNet Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage/Thermal	Riffle Stream?	FIBI score	FIBI Class	47c FIBI BIT	FIBI Pass/Fail
1319	9/21/21	1630.0	47c	MS	Und.	82	Excellent	44/65	Pass

Overall:

Community	Assessment Type	Assessment Result	Support Level	IR Category	Reason
Benthic Macroinvertebrates	Evaluated	Pass (3/5)	Full
Fish	Evaluated	Pass (1/1)	Full		Assessment was monitored because the samples used for the
Overall	Evaluated	Pass	Full	1	the assessment were collected in a recent five year period.

Class BWW1 - Continuous DO Monitoring:

Site ID	Data Source ID	# Days Monitoring (2016)	DO Criteria Type	# 2016 violations / Violations needed for impairment	Violates Annual Significantly >10% Rule?	Assessment Type	Support Level
			24 hr	1/6	No
843	6	29	16 hr	0/6	No	Evaluated	Full

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)
1068	tissue plug	2012	walleye	3	40.0	0.285
1068	tissue plug	2011	walleye	4	47.2	0.753
Support Level	Not	A historic one meal/week mercury consumption advisory for any predator fish exists on this segment. Based on IR Methodology, the Class HH (fish consumption) use was assessed as “not supported.”

Class HH-F - Toxic Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	Number of Non - Detects	Mean Value > Criterion or MCL	Assessment Type	Support Level
10120001	6	Selenium	18 / 2	2	0.8	1	8	NO	Mon	Full

Monitoring and Methods

Assessment Key Dates

8/23/2011	Fish Tissue Monitoring
8/15/2016	Biological Monitoring
1/9/2020	Monitoring Start
12/8/2022	Monitoring End
8/2/2012	Fish Tissue Monitoring
8/23/2019	Biological Monitoring
8/20/2019	Biological Monitoring
9/21/2021	Biological Monitoring
8/15/2022	Biological Monitoring

Methods

150	Monitoring data more than 5 years old
200	Physical/Chemical Monitoring
260	Fish tissue analysis
315	Regional reference site approach
320	Benthic macroinvertebrate surveys
420	Indicator bacteria monitoring

Water Quality Assessments

Impaired Waters List

Shell Rock River IA 02-SHL-783

Assessment Summary

Assessment Explanation

Assessment Key Dates

Methods