Walnut Creek IA 02-IOW-1916

confluence with unnamed tributary in NW 1/4 S24 T81N R15W Poweshiek Co. to headwaters in S10 T81N R16W Poweshiek Co.

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 2020 - 2022
Stream/River Water Quality Data	CY 2020 - 2022
Lake Water Quality Data	CY 2018 - 2022
Biological Sampling Data	CY 2018 - 2022*
Fish Kill Data	CY 2018 - 2022
Fish Tissue Sampling Data	CY 2018 - 2022
Continuous Dissolved Oxygen Sampling Data	CY 2018 - 2022
*Biological sites sampled in both 2017 and 2021 were also assessed.

Open Segment Map
View assessment methodology in new window

Cycle: 2024
Release Status: Final
Overall IR: 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trend: Unknown
Created: 11/1/2023 8:13:27 AM
Updated: 1/5/2024 1:09:07 PM

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

Moderate

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 BWW1

Presumptive Use

Aquatic Life - Warm Water Type 1

WINOFI

Biological: low fish IBI

Support Level

Further Investigation Needed

Impairment Code

3b-u - Use potentially biologically impaired based on uncalibrated IBI metrics.

Cause Magnitude

Slight

Status

Continuing

Source

Hydromodification: Hydrologic Modifications

Source Confidence

Moderate

Cycle Added

2016

Impairment Rationale

Potential Impairment

Data Source

Biological monitoring: Iowa DNR WQMA

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The presumptive Class A1 use was assessed as “not supported” due to violations of Iowa water quality criteria for indicator bacteria (E. coli). The Class BWW1 use was assessed as “WINOFI” 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).

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2010-2011	13790006	Walnut Creek at 120 St	Site 5m
Iowa DNR	6	WQ	CY 2010-2011	13790007	Walnut Creek at 80 St	Site 6
Iowa DNR	6	BIO	See Below	702	Walnut Creek	Malcolm – WLNT3

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
13790006	6	25 / 2	395	912	Yes	20	80%	Yes	Evaluated	Not
13790007	6	25 / 2	334	484	Yes	15	60%	Yes	Evaluated	Not

Presumptive Class BWW1 - 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
702	7/28/09	11.7	47f	MS/WW	ArtSub	53	Fair	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
702	7/28/09	11.7	47f	MS/WW	NA	23	Poor	36	Fail

Overall:

Community	Assessment Type	Assessment Result	Support Level	IR Category	Reason
Benthic Macroinvertebrates	Evaluated	Pass (1/1)	Full
Fish	Evaluated	Fail (0/1)	WINOFI		Assessment was evaluated because it was based on a single sample and
Overall	Evaluated	Fail	WINOFI	3bu	the drainage area of the sample site was smaller than calibrated range.

Monitoring and Methods

Assessment Key Dates

3/22/2010

Monitoring Start

9/16/2011

Monitoring End

7/28/2009

Biological Monitoring

3/9/2018

TMDL Completed

Methods

150

Monitoring data more than 5 years old

200

Physical/Chemical Monitoring

315

Regional reference site approach

320

Benthic macroinvertebrate surveys

330

Fish surveys

420

Indicator bacteria monitoring