2020 Final assessment for North Skunk River

North Skunk River IA 03-NSK-854

from confluence with Cedar Cr. (S15 T75N R12W Keokuk Co.) to confluence with Middle Cr. in S35 T76N R14W Mahaska Co.

Assessment Cycle

2020

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 2016 - 2018
Stream/River Water Quality Data	CY 2016 - 2018
Lake Water Quality Data	CY 2014 - 2018
Biological Sampling Data	CY 2014 - 2018*
Fish Kill Data	CY 2014 - 2018
Fish Tissue Sampling Data	CY 2014 - 2018
Continuous Dissolved Oxygen Sampling Data	CY 2014 - 2018
*Biological sites sampled in both 2013 and 2017 were also assessed.

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

Created: 9/9/2020 9:05:37 AM
Updated: 10/12/2020 2:39:23 PM

Assessment conducted in accordance with Iowa's 2020 IR methodology

Use Support

Class A1

Partially Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Partially 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 IV

Class BWW2

Not Supported

Metals: Chromium

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

2010

Impairment Rationale

Violations of acute criterion

Data Source

Ambient monitoring: Iowa DNR-rivers

TMDL Priority

Tier III

General Use

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed as "partially supported" due to levels of indicator bacteria (E. coli) that exceeded state water quality criteria. The Class BWW2 use remains assessed as "not supported" due to violations of state water quality criteria for chromium.

Assessment Explanation

Sources of Data:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2004-2006, 2016-2018	10540001	North Skunk River
Iowa DNR	6	BIO	See Below	944	North Skunk River	Sigourney

Class A1 - Indicator Bacteria:

Site ID	Data Source ID	# Samples / # Years	2016 Geometric Mean	2017 Geometric Mean	2018 Geometric Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
10540001	6	22 / 3	408.24	407.73	246.52	Yes	12	55%	Yes	Monitored	Partial

Class A1 - pH:

Site ID	Data Source ID	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
10540001	6	36 / 3	8.5	8	8.1	0	0%	No	Monitored	Full

Class BWW2 - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Acute / Chronic Violations	% Acute/ Chronic Violations	Significantly >10% Violations	Assessment Type	Support Level
10540001	6	Ammonia	36 / 3	0.53	0.08	0.02	0 / 0	0% / 0%	No	Monitored	Full
10540001	6	Chloride	36 / 3	53	23	20	0 / 0	0% / 0%	No	Monitored	Full
10540001	6	Dissolved oxygen	36 / 3	13.7	10.1	9.9	NA / 1	NA / 3%	No	Monitored	Full
10540001	6	pH	36 / 3	8.5	8	8.1	0 / NA	0% / NA	No	Monitored	Full
10540001	6	Sulfate	36 / 3	150	29.3	24	0 / NA	0% / NA	No	Monitored	Full
10540001	6	Temperature	36 / 3	25.6	12.3	10	0 / 0	0% / 0%	No	Monitored	Full

Class BWW2 - Toxic Parameters: 2004-2006

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Acute / Chronic Violations	% Acute/ Chronic Violations	>1 Acute / Chronic Violation	Assessment Type	Support Level
10540001	6	Aluminum	9 / 2	6.2	1.961	0.92	0 / 0	0% / 0%	No	Evaluated	Full
10540001	6	Arsenic	9 / 2	2.2	1.49	1.5	0 / 0	0% / 0%	No	Evaluated	Full
10540001	6	Cadmium	9 / 2	0.05	0.028	0.025	0 / 0	0% / 0%	No	Evaluated	Full
10540001	6	Chromium	9 / 2	1.3	0.74	0.76	0 / 0	0% / 0%	No	Evaluated	Full
10540001	6	Copper	9 / 2	2.5	1.46	1.4	0 / 0	0% / 0%	No	Evaluated	Full
10540001	6	Lead	9 / 2	0.27	0.095	0.07	0 / 0	0% / 0%	No	Evaluated	Full
10540001	6	Nickel	9 / 2	4.3	3	2.9	0 / 0	0% / 0%	No	Evaluated	Full
10540001	6	Selenium	9 / 2	2	1.26	1.1	0 / 0	0% / 0%	No	Evaluated	Full
10540001	6	Zinc	9 / 2	2.3	1.2	1.2	0 / 0	0% / 0%	No	Evaluated	Full
During the 2004-2006 period, two samples contained 0.02 mg/l of total chromium and exceeded the Class BWW1 aquatic life acute criterion of 0.016 mg/l. Based on Iowa DNR’s assessment/listing methodology, more than one violation of an acute water quality criterion for a toxic parameter over a three-year period suggests impairment of aquatic life uses.

Class BWW2 - Biological Sampling:

Benthic Macroinvertebrates:

BioNet Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage/Thermal	BM Sample Gear	BMIBI score	BMIBI Class	47f BMIBI BIT	BMIBI Pass/ Fail
944	10/12/15	631	47f	MS/WW	Float ArtSub	69	Good	51	Pass
944	8/21/14	631	47f	MS/WW	Float ArtSub	56	Good	51	Pass

Overall:

Community	Assessment Type	Assessment Result	Support Level	Earned IR Category	Actual IR Category	Reason
Benthic Macroinvertebrates	Evaluated	Pass (2/2)	Full	1	1	Assessment is evaluated because the drainage area of the sample site was larger than the calibrated range.

Monitoring and Methods

Assessment Key Dates

8/21/2014	Biological Monitoring
1/7/2004	Fixed Monitoring Start Date
12/4/2006	Fixed Monitoring End Date
1/6/2016	Fixed Monitoring Start Date
12/10/2018	Fixed Monitoring End Date
10/12/2015	Biological Monitoring

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

Water Quality Assessments

Impaired Waters List

North Skunk River IA 03-NSK-854

Assessment Summary

Assessment Explanation

Assessment Key Dates

Methods