West Nishnabotna River IA 05-NSH-1441

from confluence with Silver Cr. (S21 T71N R41W Mills Co.) to confluence Farm Cr. in S9 T73N R40W Mills Co.

Assessment Cycle

2022

Release Status

Final

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 2018 - 2020
Stream/River Water Quality Data	CY 2018 - 2020
Lake Water Quality Data	CY 2016 - 2020
Biological Sampling Data	CY 2016 - 2020*
Fish Kill Data	CY 2016 - 2020
Fish Tissue Sampling Data	CY 2016 - 2020
Continuous Dissolved Oxygen Sampling Data	CY 2016 - 2020
*Biological sites sampled in both 2015 and 2019 were also assessed.

Overall IR Category: 5 - Water is impaired or threatened and a TMDL is needed.
Trend: Unknown

Created: 12/27/2021 2:55:16 PM
Updated: 1/13/2022 3:13:03 PM

Assessment conducted in accordance with Iowa's 2022 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

N/A

Cycle Added

2008

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Ambient monitoring: Iowa DNR-rivers

TMDL Priority

Tier III

Class BWW1

Aquatic Life

Warm Water Type 1

WINOFI

Further Investigation Needed

Support Level

Water in Need of Further Investigation (WINOFI)

Impairment Code

3b-u - Use potentially biologically impaired based on uncalibrated IBI metrics.

Cause Magnitude

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2014

Impairment Rationale

Low Biotic Index

Data Source

Biological monitoring: Iowa DNR WQMA

Class HH

Human Health

Not Assessed

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 "WINOFI" based on biological sampling data. All other designated uses were "not assessed."

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2014-2016, CY 2018-2020	10650001	West Nishnabotna River near Malvern
Iowa DNR	6	BIO	See Below	935	West Nishnabotna River	Malvern

Class A1 - Indicator Bacteria:

Site ID	Data Source ID	# Samples / # Years	2014 Geo. Mean	2015 Geo. Mean	2016 Geo. Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
10650001	6	24 / 3	1295	1293	661	Yes	18	75%	Yes	Evaluated	Not

Class A – 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
10650001	6	36 / 3	7.2	8.5	8.1	0	7	NO	Monitored	Full

Class BWW1 - Conventional 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
10650001	6	Ammonia	36 / 3	0.02	0.76	0.06	NA	0 / 0	7	NO	Monitored	Full
10650001	6	Chloride	36 / 3	11	23	16	NA	0 / 0	7	NO	Monitored	Full
10650001	6	Dissolved Oxygen	36 / 3	7.3	13.3	10.2	0	NA / NA	7	NO	Monitored	Full
10650001	6	pH	36 / 3	7.2	8.5	8.1	0	NA / NA	7	NO	Monitored	Full
10650001	6	Sulfate	36 / 3	12	42	26	0	NA / NA	7	NO	Monitored	Full
10650001	6	Temperature	36 / 3	0	29.7	13.2	0	NA / NA	7	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
10650001	6	Aluminum	14 / 3	18	4.39	2.45	0 / 0	NO	Monitored	Full
10650001	6	Arsenic	13 / 3	3.5	2.5	2.4	0 / 0	NO	Monitored	Full
10650001	6	Cadmium	13 / 3	0.025	0.025	0.025	0 / 0	NO	Monitored	Full
10650001	6	Chromium	13 / 3	1.4	0.8	0.8	0 / 0	NO	Monitored	Full
10650001	6	Lead	13 / 3	0.24	0.11	0.1	0 / 0	NO	Monitored	Full
10650001	6	Nickel	13 / 3	3.6	2.8	2.7	0 / 0	NO	Monitored	Full
10650001	6	Silver	13 / 3	0.025	0.025	0.025	0 / 0	NO	Monitored	Full
10650001	6	Zinc	13 / 3	4.4	2.2	2.4	0 / 0	NO	Monitored	Full

Class BWW1 - Biological Sampling:

Benthic Macroinvertebrates:

Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage	BM Sample Gear	BMIBI score	BMIBI Class	47e BMIBI BIT	BMIBI Pass/Fail
935	8/13/20	967	47e	MO	Floating Art Sub	22	Poor	54	Fail
935	9/7/16	967	47e	MO	Floating Art Sub	42	Fair	54	Fail

Overall:

Community	Assessment Type	Assessment Result	Support Level	IR Category	Reason
Benthic Macroinvertebrates	Evaluated	Fail (0/2)	Not		Assessment was evaluated because the drainage area of the sample site
Overall	Evaluated	Fail	WINOFI	3bu	was greater than the calibrated range.

Class HH - No Data

Monitoring and Methods

Assessment Key Dates

8/13/2020

Biological Monitoring

1/7/2014

Fixed Monitoring Start Date

12/6/2016

Fixed Monitoring End Date

9/7/2016

Biological Monitoring

1/8/2018

Fixed Monitoring Start Date

12/1/2020

Fixed Monitoring End Date

Methods

150

Monitoring data more than 5 years old

230

Fixed station physical/chemical (conventional plus toxic pollutants)

315

Regional reference site approach

320

Benthic macroinvertebrate surveys

420

Indicator bacteria monitoring