Indian Creek IA 06-BSR-1531

mo to trib S33T94NR47W Sioux 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: 7/30/2019 12:15:09 PM
Updated: 7/30/2019 12:16:44 PM

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Moderate

Cycle Added

2008

Impairment Rationale

Geometric mean criterion exceeded

Data Source

TMDL monitoring: Iowa DNR

TMDL Priority

Tier III

Class BWW2

Aquatic Life - Warm Water Type 2

Fully Supported

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 "not supported" due levels of indicator bacteria that exceed Iowa water quality criteria. The Class B(WW2) aquatic life uses remain assessed as "fully supported". This assessment remains based on results of monitoring conducted in support of TMDL development during the 2002-2004 assessment period. The data used for this assessment were generated from the DNR/SHL station near Chatsworth (station 9) monitored during the 2002-2004 assessment period in support of TMDL development (STORET station 11750001).

Assessment Explanation

The presumptive Class A1 uses remain assessed (evaluated) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric mean level of indicator bacteria (E. coli) in the 23 samples collected at the DNR/SHL TMDL monitoring near Chatsworth during summer recreational seasons of 2002-2003 (564 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Fourteen of the 24 samples (61%) exceed Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and according to DNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Because these data are now more than five years old, and because as data age beyond five years they are less able to represent current water quality conditions, the assessment type is changed from “monitored” (a higher confidence assessment) to “evaluated” (lower confidence assessment.)

Regarding support of the Class B(WW2) aquatic life uses, results of ambient monitoring at the DNR/SHL station from March to December 2003 showed no violations of Class B(WW2) water quality criteria for ammonia-nitrogen, dissolved oxygen, or pH in the 22 samples collected. Based on these data, the Class B(WW2) aquatic life uses remain assessed (monitored) as “fully supported.”

Monitoring and Methods

Assessment Key Dates

3/19/2002

Fixed Monitoring Start Date

12/16/2003

Fixed Monitoring End Date

Methods

150

Monitoring data more than 5 years old

240

Non-fixed station physical/chemical (conventional + toxicants)

420

Indicator bacteria monitoring