Iowa DNR
ADBNet

Water Quality Assessments

Impaired Waters List

East Indian Creek IA 03-SSK-947

mouth to trib S34T85NR22W Story Co.

Assessment Cycle
2018
Release Status
Final
Cycle Period
2014 - 2016
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
WINOFI
Bacteria: Indicator Bacteria- E. coli
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
Not Assessed
General Use
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 Water column surveys (e.g. fecal coliform)
860 Other Agencies/Organizations provided monitoring data