2022 Final assessment for Skunk River

Skunk River IA 03-SKU-889

mouth to confluence with Big Cr. southeast of Mt. Pleasant in S19 T70N R5W in Henry 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: 12/22/2021 11:27:58 AM
Updated: 1/5/2022 9:35:43 AM

Assessment conducted in accordance with Iowa's 2022 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

N/A

Cycle Added

2012

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 exceeded state water quality criteria. The Class BWW1 use was assessed as "fully supported" based on biological sampling data and water quality monitoring data. The Class HH use was assessed as "fully supported" based on fish tissue 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 2018-2020	10560002	Skunk River near Augusta
USGS	11	WQ	CY 2018-2018	5474000	Skunk River at Augusta, IA
Iowa DNR	6	BIO	See Below	943	Skunk River	Augusta
Iowa DNR	6	FT	See Below	171	Skunk River	NE of Weaver

Class A1 - Indicator Bacteria:

Site ID

Data Source ID

# Samples per Year (2018/ 2019/2020)

2018 Geometric Mean

2019 Geometric Mean

2020 Geometric Mean

Violates Annual Geometric Mean?

# 2018 SSM violations / SSM Violations needed for impairment

# 2019 SSM violations / SSM Violations needed for impairment

# 2020 SSM violations / SSM Violations needed for impairment

Violates Annual SSM Significantly >10% Rule?

Assessment Type

Support Level

10560002

8/8/8

322

175

YES

2 / 3

3 / 3

4 / 3

YES

Monitored

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
10560002	6	36 / 3	6.9	9	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
10560002	6	Ammonia	36 / 3	0.025	1.2	0.1	NA	0 / 0	7	NO	Monitored	Full
10560002	6	Chloride	36 / 3	7.8	48	21.5	NA	0 / 0	7	NO	Monitored	Full
10560002	6	Dissolved Oxygen	36 / 3	5.9	16.3	10.6	0	NA / NA	7	NO	Monitored	Full
10560002	6	pH	36 / 3	6.9	9	8.1	0	NA / NA	7	NO	Monitored	Full
10560002	6	Sulfate	36 / 3	9.6	85	28.7	0	NA / NA	7	NO	Monitored	Full
10560002	6	Temperature	36 / 3	0	29.3	12.8	0	NA / NA	7	NO	Monitored	Full
5474000	11	Temperature	568 / 3	0	29	15	0	NA / NA	67	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
10560002	6	Aluminum	14 / 3	26	4.379	1.075	0 / 0	NO	Monitored	Full
10560002	6	Arsenic	13 / 3	3	1.63	1.5	0 / 0	NO	Monitored	Full
10560002	6	Cadmium	13 / 3	0.07	0.03	0.02	0 / 0	NO	Monitored	Full
10560002	6	Chromium	13 / 3	1.1	0.7	0.7	0 / 0	NO	Monitored	Full
10560002	6	Lead	13 / 3	0.36	0.17	0.15	0 / 0	NO	Monitored	Full
10560002	6	Nickel	13 / 3	5.5	3.1	2.9	0 / 0	NO	Monitored	Full
10560002	6	Silver	13 / 3	0.025	0.025	0.025	0 / 0	NO	Monitored	Full
10560002	6	Zinc	13 / 3	3	1.66	1.9	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	40a BMIBI BIT	BMIBI Pass/Fail
943	8/29/19	4303	40a	MS	Hess	60	Good	41	Pass

Overall:

Community	Assessment Type	Assessment Result	Support Level	IR Category	Reason
Benthic Macroinvertebrates	Evaluated	Pass (1/1)	Full		Assessment was evaluated because the drainage area of the site used for
Overall	Evaluated	Pass	Full	1	the assessment was greater than the calibrated range.

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)
171	whole	2016	common carp	5	59.3	0.08	0.05	0.06
Support Level	Full

Monitoring and Methods

Assessment Key Dates

1/2/2018	Fixed Monitoring Start Date
12/26/2020	Fixed Monitoring End Date
8/29/2019	Biological Monitoring
9/14/2016	Fish Tissue Monitoring

Methods

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

Skunk River IA 03-SKU-889

Assessment Summary

Assessment Explanation

Assessment Key Dates

Methods