2022 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.

2022
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 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.

Open Segment Map
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Overall IR

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

Trend

Unknown

Created

12/15/2021 10:16:18 AM by

Updated

12/15/2021 10:19:15 AM 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

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2012

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Special project/study

Class BWW2

Aquatic Life - Warm Water Type 2

Not Supported

Biological: low fish IBI

Support Level

Not 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

303(d) Delistings for this Cycle

No delistings for this assessment cycle.

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 was assessed as “not 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 presumptive 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

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	BIO	See Below	1231	Walnut Creek	NW of Hartwick – REMAP #418
Iowa DNR	6	BIO	See Below	200	Walnut Creek	Holiday Lake
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

Presumptive Class A1 – Indicator Bacteria: 2010-2011

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	Not
13790004	6	25 / 2	541	917	Yes	21	84%	Yes	Evaluated	Not

Class BWW2 - Biological Sampling:

Benthic Macroinvertebrates:

Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage	BM Sample Gear	BMIBI score	BMIBI Class	47f BMIBI BIT	BMIBI Pass/ Fail
1231	8/15/19	40.7	47f	MS	Art Sub	58	Good	51	Pass
200	8/25/10	34.9	47f	MS	Art Sub	54	Fair	51	Pass

Fish:

Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage	Riffle Stream?	FIBI score	FIBI Class	47f FIBI BIT	FIBI Pass/ Fail
1231	8/15/19	40.7	47f	MS	NA	40	Fair	36	Pass
200	8/25/10	34.9	47f	MS	NA	25	Poor	36	Fail

Overall:

Community	Assessment Type	Assessment Result	Support Level	IR Category	Reason
Benthic Macroinvertebrates	Evaluated	Pass (2/2)	Full
Fish	Evaluated	Fail (1/2)	Not	5bt	Assessment was evaluated because it included samples not collected
Overall	Evaluated	Fail	Not		in the last five years.

Monitoring and Methods

Assessment Key Dates

8/25/2010

Biological Monitoring

1/13/2010

Fixed Monitoring Start Date

9/16/2011

Fixed Monitoring End Date

3/9/2018

TMDL Completed

8/15/2019

Biological Monitoring

Methods

150

Monitoring data more than 5 years old

315

Regional reference site approach

320

Benthic macroinvertebrate surveys

330

Fish surveys

380

Quantitative physical habitat assessment

420

Indicator bacteria monitoring