Turkey Creek IA 04-UDM-6543

from Big Creek Lake (T81N R25W Sec14 Polk Co.) to headwaters (T81N R25W Sec1 Polk 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 2014 - 2016
Stream/River Water Quality Data	CY 2014 - 2016
Lake Water Quality Data	CY 2012 - 2016
Biological Sampling Data	CY 2012 - 2016*
Fish Kill Data	CY 2012 - 2016
Fish Tissue Sampling Data	CY 2012 - 2016
Continuous Dissolved Oxygen Sampling Data	CY 2012 - 2016
*Biological sites sampled in both 2011 and 2015 were also assessed.

Open Segment Map
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Cycle: 2018
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trend: Unknown
Created: 7/19/2019 10:38:24 AM
Updated: 7/19/2019 10:39:47 AM

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Partially Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Partially Supported

Impairment Code

5p - Impairment occurs on a waterbody with a presumptive A1 or B(WW1) use.

Cause Magnitude

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2014

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Special project/study: Iowa DNR

TMDL Priority

Tier III

Class BWW1

Presumptive Use

Aquatic Life - Warm Water Type 1

Not Assessed

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The presumptive Class A1 (primary contact recreation) uses remain assessed as “partially supported” due to violations of Iowa water quality criteria for indicator bacteria. The presumptive Class B(WW1) aquatic life uses remain "not assessed" due to the lack of sufficient water quality information upon which to base an assessment. The source of data for this assessment is the results of monitoring at STORET station 13770006 (BCW-11) conducted as part of a Clean Water Act Section 319 water quality project from March to September 2011. Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment categories are considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).

Assessment Explanation

The presumptive Class A1 uses are assessed (evaluated) as “partially supported" due to levels of indicator bacteria (E. coli) that slightly exceed the Class A1 geometric mean criterion. The geometric mean of indicator bacteria (E. coli) in the seven samples collected at Site BCW-11 during the recreation season of 2011 was 324 orgs/100 ml. Four of the seven samples (57%) exceeded the Class A1 single sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if a recreation season geometric mean is greater than the respective criterion (126 orgs/100 ml for Class A1), the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).

Monitoring and Methods

Assessment Key Dates

3/28/2011

Fixed Monitoring Start Date

9/28/2011

Fixed Monitoring End Date

Methods

150

Monitoring data more than 5 years old

420

Indicator bacteria monitoring