East Indian Creek IA 03-SSK-947

mouth to trib S34T85NR22W Story Co.

Assessment Cycle

2018

Release Status

Final

Data Collection Period

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.

Overall IR Category: 3 - Insufficient data exist to determine whether any designated uses are met.
Trend: Unknown

Created: 9/12/2019 1:06:36 PM
Updated: 2/13/2020 2:03:40 PM

Assessment conducted in accordance with Iowa's 2018 IR methodology

Use Support

Class A1

Recreation

Primary contact

Presumptive Use

WINOFI

Further Investigation Needed

Support Level

Water in Need of Further Investigation (WINOFI)

Impairment Code

3b - Use potentially impaired based on an evaluated assessment.

Cause Magnitude

Moderate

Status

New

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2018

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Special project/study

Class BWW2

Aquatic Life

Warm Water Type 2

Not Assessed

General Use

General Use water

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 (primary contact recreation) use is assessed (evaluated) as "not supported” due to high levels of indicator bacteria (E. coli) that exceed state water quality criteria. All other uses are "not assessed".

Assessment Explanation

The Class A1 (primary contact recreation) use is assessed (evaluated) as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric mean of indicator bacteria (E. coli) in the samples collected during the 2016 recreational season (1234 orgs/100 ml) exceeded the Class A1 criterion of 126 orgs/100 ml. All 14 samples (100%) collected during the 2014-2016 period exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and Iowa DNR’s assessment/listing methodology, if the geometric mean is greater than 126 orgs/100 ml., the Class A1 primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).

The bacteria samples were collected by the Prairie Rivers Watershed Group and Story County Conservation with the analyses conducted by the City of Ames.Since the data were not collected under a DNR-approved quality assurance plan, the assessment was considered "evaluated" instead of "monitored".According to Iowa DNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). The Iowa DNR does, however, consider these impairments as appropriate for listing under Category 3b of the Integrated Report (waters potentially impaired and in need of further investigation).

Monitoring and Methods

Assessment Key Dates

4/27/2016

Non-fixed Monitoring Start Date

10/12/2016

Non-fixed Monitoring End Date

Methods

420

Indicator bacteria monitoring

860

Other Agencies/Organizations provided monitoring data