South Skunk River IA 03-SSK-931

from confluence with Indian Creek (S32 T80N R20W Jasper Co.) to outfall of Ames wastewater treatment plant in SW 1/4 S32 T83N R23W Story 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 1:28:08 PM
Updated: 10/16/2020 10:42:53 AM

Assessment conducted in accordance with Iowa's 2020 IR methodology

Use Support

Class A1

Recreation

Primary contact

Partially Supported

Impairments

Support Level

Partially Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

High

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 BWW2

Aquatic Life

Warm Water Type 2

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

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2004

Impairment Rationale

Low Biotic Index

Data Source

Biological monitoring: Iowa DNR WQMA

General Use

General Use water

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 violated state water quality criteria. The Class BWW2 use remains assessed as "partially supported" based on biological sampling data.

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 2016-2018	10850002	South Skunk River near Cambridge (DS1)
Iowa DNR	6	BIO	See Below	286	South Skunk River	Cambridge

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
10850002	6	21 / 3	242.75	292.74	564.27	Yes	13	62%	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
10850002	6	35 / 3	8.5	8.1	8.2	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
10850002	6	Ammonia	35 / 3	1.3	0.09	0.02	0 / 0	0% / 0%	No	Monitored	Full
10850002	6	Chloride	36 / 3	81	32	26	0 / 0	0% / 0%	No	Monitored	Full
10850002	6	Dissolved oxygen	36 / 3	13.5	10.2	9.8	NA / 0	NA / 0%	No	Monitored	Full
10850002	6	pH	35 / 3	8.5	8.1	8.2	0 / NA	0% / NA	No	Monitored	Full
10850002	6	Sulfate	36 / 3	97	37.1	29.5	0 / NA	0% / NA	No	Monitored	Full
10850002	6	Temperature	36 / 3	28.4	12.2	12.1	0 / 0	0% / 0%	No	Monitored	Full

Class BWW2 - Toxic Parameters:

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
10850002	6	Aluminum	9 / 2	4.5	1.666	1.2	0 / 0	0% / 0%	No	Evaluated	Full
10850002	6	Arsenic	9 / 2	2.3	1.64	1.6	0 / 0	0% / 0%	No	Evaluated	Full
10850002	6	Cadmium	9 / 2	0.05	0.028	0.025	0 / 0	0% / 0%	No	Evaluated	Full
10850002	6	Chromium	9 / 2	1.4	0.88	0.96	0 / 0	0% / 0%	No	Evaluated	Full
10850002	6	Copper	9 / 2	5.2	1.94	1.6	0 / 0	0% / 0%	No	Evaluated	Full
10850002	6	Lead	9 / 2	0.16	0.091	0.09	0 / 0	0% / 0%	No	Evaluated	Full
10850002	6	Nickel	9 / 2	4.9	3.4	3.1	0 / 0	0% / 0%	No	Evaluated	Full
10850002	6	Selenium	9 / 2	2.4	1.42	1.3	0 / 0	0% / 0%	No	Evaluated	Full
10850002	6	Zinc	9 / 2	12	4	2.2	0 / 0	0% / 0%	No	Evaluated	Full

Class BWW2 - Biological Sampling:

Benthic Macroinvertebrates:

BioNet Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage/Thermal	BM Sample Gear	BMIBI score	BMIBI Class	47b BMIBI BIT	BMIBI Pass/ Fail
286	8/17/16	605	47b	MS/WW	Float ArtSub	55	Fair	62	Fail
286	7/21/15	605	47b	MS/WW	Float ArtSub	75	Good	62	Pass
286	10/7/14	605	47b	MS/WW	Float ArtSub	47	Fair	62	Fail

Overall:

Community	Assessment Type	Assessment Result	Support Level	Earned IR Category	Actual IR Category	Reason
Benthic Macroinvertebrates	Evaluated	Fail (1/3)	Partial	3bu	3bu	Assessment is evaluated because the drainage area of the sample site was larger than the calibrated range.

Monitoring and Methods

Assessment Key Dates

10/7/2014

Biological Monitoring

1/7/2016

Fixed Monitoring Start Date

12/5/2018

Fixed Monitoring End Date

7/21/2015

Biological Monitoring

8/7/2016

Biological Monitoring

Methods

230

Fixed station physical/chemical (conventional plus toxic pollutants)

315

Regional reference site approach

320

Benthic macroinvertebrate surveys

420

Indicator bacteria monitoring