2020 Final assessment for West Fork Little Sioux River

West Fork Little Sioux River IA 06-LSR-1598

mouth (S12 T84N R45W Monona Co.) to confluence with a small unnamed tributary near Climbing Hill in S16 T87N R45W Woodbury 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: Stable

Created: 9/22/2020 8:38:03 AM
Updated: 10/19/2020 7:19:06 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

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2008

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Ambient monitoring: Iowa DNR-rivers

TMDL Priority

Tier III

Class BWW2

Fully Supported

General Use

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use remains assessed as "partially supported" due to levels of indicator bacteria (E. coli) that violated state water quality criteria. The Class BWW2 use was assessed as "fully supported" based on biological sampling data and water quality monitoring 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 2014-2016	10970002	West Fork Ditch at Hornick
Iowa DNR	6	BIO	See Below	934	West Fork Little Sioux River	Hornick

Class A1 - Indicator Bacteria:

Site ID	Data Source ID	# Samples / # Years	2014 Geometric Mean	2015 Geometric Mean	2016 Geometric Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
10970002	6	23 / 3	351	633	614	Yes	16	70%	Yes	Evaluated	Partial

Class A - pH:

Site ID	Data Source ID	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
10970002	6	35 / 3	8.5	8.2	8.2	0	0%	No	Evaluated	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
10970002	6	Ammonia	35 / 3	0.16	0.03	0.02	0 / 0	0% / 0%	No	Evaluated	Full
10970002	6	Chloride	35 / 3	24	19	19	0 / 0	0% / 0%	No	Evaluated	Full
10970002	6	Dissolved oxygen	35 / 3	15.2	10.3	9.9	NA / 0	NA / 0%	No	Evaluated	Full
10970002	6	pH	35 / 3	8.5	8.2	8.2	0 / NA	0% / NA	No	Evaluated	Full
10220002	6	Sulfate	35 / 3	100	72	74	0 / NA	0% / NA	No	Evaluated	Full
10220002	6	Temperature	35 / 3	23.9	11.8	12.6	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	47d BMIBI BIT	BMIBI Pass/ Fail
934	8/18/14	399	47d	MO/WW	Float ArtSub	58	Good	54	Pass
934	7/30/13	399	47d	MO/WW	Float ArtSub	61	Good	54	Pass

Overall Assessment:

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 it included samples not collected in the last five years.

Monitoring and Methods

Assessment Key Dates

1/8/2014	Fixed Monitoring Start Date
12/7/2016	Fixed Monitoring End Date
7/30/2013	Biological Monitoring
8/18/2014	Biological Monitoring

Methods

150	Monitoring data more than 5 years old
210	Fixed station physical/chemical monitoring (conventional pollutants only)
315	Regional reference site approach
320	Benthic macroinvertebrate surveys
420	Indicator bacteria monitoring

Water Quality Assessments

Impaired Waters List

West Fork Little Sioux River IA 06-LSR-1598

Assessment Summary

Assessment Explanation

Assessment Key Dates

Methods