2024 Pending assessment for Thompson River

Thompson River IA 05-GRA-1351

from the Iowa/Missouri state line to confluence with Long Cr. in SW 1/4 S8 T69N R26W Decatur 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 8:13:00 AM
Updated: 12/21/2023 9:29:46 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

2004

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Ambient monitoring: Iowa DNR-rivers

TMDL Priority

Tier III

Class BWW1

Fully Supported

Class HH

Fully Supported

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 BWW1 use was assessed as "fully supported" based on biological sampling data and on water quality monitoring data. The Class HH use was assessed as "fully supported" based on water quality monitoring 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	10270001	Thompson Fork - Grand River at Davis City
Iowa DNR	6	BIO	See Below	266	Thompson River	Decatur City
Iowa DNR	6	BIO	See Below	932	Thompson Fork - Grand River	Davis City

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

10270001

8/8/8

122

148

578

YES

2 / 3

5 / 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
10270001	6	35 / 3	7	8.3	7.8	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
10270001	6	Chloride	36 / 3	8.6	23	12.9	NA	0 / 0	7	NO	Mon	Full
10270001	6	Dissolved Oxygen	36 / 3	5.4	14	9.8	0	NA / NA	7	NO	Mon	Full
10270001	6	pH	35 / 3	7	8.3	7.8	0	NA / NA	7	NO	Mon	Full
10270001	6	Sulfate	36 / 3	12	40	24	0	NA / NA	7	NO	Mon	Full
10270001	6	Temperature	36 / 3	0	30.9	12.4	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
10270001	6	Ammonia	35 / 3	0.35	0.05	0.02	0 / 0	NO	Mon	Full
10270001	6	Cadmium	20 / 3	0.5	0.5	0.5	0 / 0	NO	Mon	Full
10270001	6	Chromium	20 / 3	5	0.77	0.5	0 / 0	NO	Mon	Full
10270001	6	Lead	20 / 3	1	0.91	1	0 / 0	NO	Mon	Full
10270001	6	Nickel	20 / 3	4.1	2.2	2.2	0 / 0	NO	Mon	Full
10270001	6	Selenium	18 / 2	2	0.6	0.5	0 / 0	NO	Mon	Full
10270001	6	Silver	20 / 3	1	0.902	1	0 / 0	NO	Mon	Full
10270001	6	Zinc	20 / 3	4	0.9	0.5	0 / 0	NO	Mon	Full

Class BWW1 - Biological Sampling:

Benthic Macroinvertebrates:

BioNet Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage	BM Sample Gear	BMIBI score	BMIBI Class	40a BMIBI BIT	BMIBI Pass/Fail
932	8/3/22	701.0	40a	MO	Surber	60	Good	41	Pass
266	7/28/22	601.7	40a	MO	Surber	69	Good	41	Pass
932	7/20/18	701.0	40a	MO	Hess	48	Fair	41	Pass

Fish:

BioNet Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage	Riffle Stream?	FIBI score	FIBI Class	40a FIBI BIT	FIBI Pass/Fail
266	7/28/22	601.7	40a	MO	NA	43	Fair	33	Pass

Overall:

Community	Assessment Type	Assessment Result	Support Level	IR Category	Reason
Benthic Macroinvertebrates	Evaluated	Pass (3/3)	Full
Fish	Evaluated	Pass (1/1)	Full		Assessment was evaluated because the drainage areas of the
Overall	Evaluated	Pass	Full	1	sample sites were greater than the calibrated range.

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
10270001	6	Selenium	18 / 2	2	0.6	0.5	15	NO	Mon	Full

Monitoring and Methods

Assessment Key Dates

7/28/2022	Biological Monitoring
7/20/2018	Biological Monitoring
1/6/2020	Monitoring Start
12/1/2022	Monitoring End
8/3/2022	Biological Monitoring

Methods

200	Physical/Chemical Monitoring
315	Regional reference site approach
320	Benthic macroinvertebrate surveys
330	Fish surveys
420	Indicator bacteria monitoring

Water Quality Assessments

Impaired Waters List

Thompson River IA 05-GRA-1351

Assessment Summary

Assessment Explanation

Assessment Key Dates

Methods