2020 assessment for Walnut Creek

Walnut Creek IA 04-RAC-1120

mouth (S13 T78 R25W Polk Co.) to Interstate 35/80 in S33 T79N R25W Polk 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

4 - Water is impaired or threatened and a TMDL has been completed or is not needed.

Trend

Unknown

Created

8/12/2020 9:04:12 AM by

Updated

10/13/2020 6:46:37 AM by

Use Support

Class A1

Recreation - Primary contact

Partially Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Partially 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

2010

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Volunteer monitoring

Class BWW2

Aquatic Life - Warm Water Type 2

Not Assessed

General Use

General Use water -

Not Assessed

303(d) Delistings for this Cycle

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use remains assessed as “partially supported” based levels of indicator bacteria (E. coli) that exceeded state water quality criteria. All other designated uses were "not assessed". Note: A TMDL for pathogen indicator (E. coli) impairments in the Raccoon River basin was prepared by DNR and approved by EPA in June 2008; therefore, this impairment remains in Category 4a of Iowa’s Integrated Report.

Assessment Explanation

Sources of Data:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
IASNAPST	4	WQ	CY 2014-2016	977111	Walnut Creek - Site WC2	Polk County Snapshot
IASNAPST	4	WQ	CY 2014-2016	977113	Walnut Creek - Site WC4	Polk County Snapshot
IASNAPST	4	WQ	CY 2014-2016	977115	Walnut Creek - Site WC6	Polk County Snapshot

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
977111	4	6 / 3	192	322	173	Yes	3	50%	Yes	Evaluated	Partial
977113	4	6 / 3	124	401	249	Yes	4	67%	Yes	Evaluated	Partial
977115	4	6 / 3	177	401	228	Yes	4	67%	Yes	Evaluated	Partial

Class BWW2 - No Data

Monitoring and Methods

Assessment Key Dates

5/7/2014

Non-fixed Monitoring Start Date

10/4/2016

Non-fixed Monitoring End Date

6/1/2008

TMDL Completed

Methods

420

Indicator bacteria monitoring