2020 assessment for Walnut Creek

Walnut Creek IA 02-IOW-709

from confluence with North Walnut Cr. (S7 T81N R13W Poweshiek Co.) to confluence with unnamed tributary in NW 1/4 S24 T81N R15W Poweshiek Co.

2020
Open Data Collection Period Modal

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.

Open Segment Map
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Overall IR

5 - Water is impaired or threatened and a TMDL is needed.

Trend

Unknown

Created

9/4/2020 9:08:52 AM by

Updated

10/12/2020 1:01:37 PM by

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

4a - Pollutant-caused impairment. TMDL has been completed.

Cause Magnitude

High

303(d) Listing Status

Delisted

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2012

Impairment Rationale

Geometric mean criterion exceeded

Cycle Delisted

2020

Delisting Rationale

TMDL preparation and approval

Data Source

Special project/study

Class BWW2

Aquatic Life - Warm Water Type 2

Partially Supported

Biological: low fish IBI

Support Level

Partially Supported

Impairment Code

5b-t - Biological - tentative

Cause Magnitude

Moderate

303(d) Listing Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2004

Impairment Rationale

Low Biotic Index

Data Source

Biological monitoring: Iowa DNR WQMA

TMDL Priority

Tier IV

General Use

General Use water -

Not Assessed

303(d) Delistings for this Cycle

Cycle Added	Class	Cause	Data Source	Rationale
2012	Class A1	Bacteria: Indicator Bacteria- E. coli	Special project/study	TMDL preparation and approval

Documentation

Assessment Summary

The presumptive Class A1 use remains assessed as “not supported” due to levels of indicator bacteria (E. coli) that exceeded state water quality criteria. The Class BWW2 use remains assessed as “partially supported” based on biological sampling data. Note: A TMDL covering the bacteria impairments for all segments, with the segment code prefix "IA 02-IOW" in the Iowa River Basin, was approved by EPA in 2018. Due to the completion of the TMDL, the IR category for the Class A1 use was changed from 5p (impaired; TMDL needed) to 4a (impaired; TMDL approved). Because not all impairments identified for this segment are covered by the TMDL, this segment remains in Category 5 of Iowa's Integrated Report (impaired; TMDL needed).

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 2010-2011	13790008	Walnut Creek near Hartwick	Site WLNT-1
Iowa DNR	6	WQ	CY 2010-2011	13790002	Walnut Creek at 328 Ave	Site 2m
Iowa DNR	6	WQ	CY 2010-2011	13790004	Walnut Creek near 150 St	Site 4m
Iowa DNR	6	BIO	See Below	200	Walnut Creek	Holiday Lake
Iowa DNR	6	BIO	See Below	701	Walnut Creek	Hartwick – WLNT1
Iowa DNR	6	BIO	See Below	703	Walnut Creek	Brooklyn – WLNT2

Presumptive Class A1 - Indicator Bacteria:

Site ID	Data Source ID	# Samples / # Years	2010 Geometric Mean	2011 Geometric Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
13790008	6	25 / 2	750	1105	Yes	22	88%	Yes	Evaluated	Not
13790002	6	25 / 2	727	977	Yes	21	84%	Yes	Evaluated	Partial
13790004	6	25 / 2	541	917	Yes	21	84%	Yes	Evaluated	Partial

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
200	8/25/10	35	47f	MS/WW	ArtSub	54	Fair	51	Pass
703	7/28/09	24	47f	MS/WW	ArtSub	62	Good	51	Pass
200	7/27/09	35	47f	MS/WW	ArtSub	57	Good	51	Pass
701	7/27/09	40	47f	MS/WW	ArtSub	63	Good	51	Pass

Fish:

BioNet Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage/Thermal	Riffle Stream?	FIBI score	FIBI Class	47f FIBI BIT	FIBI Pass/ Fail
200	8/25/10	35	47f	MS/WW	NA	25	Poor	36	Fail
703	7/28/09	24	47f	MS/WW	NA	29	Fair	36	Fail
200	7/27/09	35	47f	MS/WW	NA	26	Fair	36	Fail

Overall:

Community	Assessment Type	Assessment Result	Support Level	Earned IR Category	Actual IR Category	Reason
Benthic Macroinvertebrates	Evaluated	Pass (4/4)	Full
Fish	Evaluated	Fail (0/3)	Partial
Overall	Evaluated	Fail	Partial	3bc	5bt	Assessment is evaluated because it included samples not collected in the last five years.

Monitoring and Methods

Assessment Key Dates

7/27/2009

Biological Monitoring

7/28/2009

Biological Monitoring

8/25/2010

Biological Monitoring

1/13/2010

Fixed Monitoring Start Date

9/16/2011

Fixed Monitoring End Date

3/9/2018

TMDL Completed

Methods

150

Monitoring data more than 5 years old

315

Regional reference site approach

320

Benthic macroinvertebrate surveys

330

Fish surveys

420

Indicator bacteria monitoring