Iowa DNR
ADBNet

Water Quality Assessments

Impaired Waters List

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
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
Partially Supported
Bacteria: Indicator Bacteria- E. coli
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
WINOFI
Biological: low aquatic macroinvertebrate IBI
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
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