Iowa DNR

Water Quality Assessments

Impaired Waters List

South Raccoon River IA 04-RAC-1181

mouth (S21, T78, R27W, Dallas Co.) to confluence with Middle Raccoon R. in S9, T78N, R29W near Redfield in Dallas Co

Assessment Cycle
Release Status
Release Period
2012 - 2014
10/4/2016 7:58:20 AM
Overall IR Category
5 - Water is impaired or threatened and a TMDL is needed.
Last Updated
11/4/2016 3:38:59 PM
Use Support
Class A1
Primary contact
Partially Supporting
Bacteria: Indicator Bacteria, E. coli
Impairment Code
5a - Pollutant-caused impairment. TMDL needed.
Cause Magnitude
Unknown: Source Unknown
Source Confidence
Cycle Added
Impairment Rationale
Geometric mean criterion exceeded
Data Source
Ambient monitoring: Iowa DNR-rivers
TMDL Priority
Tier III
Class B(WW-1)
Aquatic Life
Warm Water Type 1
Fully Supporting
Class HH
Human Health
Not Assessed
General Use
General Use water
Not Assessed
Impairment Delistings
No delistings for this assessment cycle.
Assessment Summary

The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" (IR 5a) due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW1) aquatic life are assessed (monitored) as "fully supported” (IR 2a) based on results of ambient chemical/physical water quality monitoring from 2012 through 2014 and on 2012/2013 IDNR/SHL biological sampling. Fish consumption uses remain "not assessed" (IR 3a) due to the lack of fish contaminant monitoring in this river segment. The source of data for this assessment are the results of (2) IDNR/SHL ambient monthly monitoring during the 2012-2014 assessment period at STORET ambient monitoring station 10250001 (formerly station 429340) located near Redfield approximately 1 mile downriver from the confluence of Middle Raccoon and South Raccoon rivers and (2) 2012/2013 IDNR/SHL biological sampling conducted near Redfield.

Assessment Explanation

The Class A1 uses are assessed (monitored) as "partially supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric means of indicator bacteria (E. coli) in the 24 samples collected during the recreational seasons of 2012 through 2014 at IDNR station 10250001 near Redfield were as follows: the 2012 geometric mean was 157 orgs/100 ml, the 2013 geometric mean was 162 orgs/100 ml, and the 2014 geometric mean was 274 orgs/100 ml. All three geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml. Nine of the 25 samples (36%) 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 IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”

The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported” based on results of IDNR/SHL ambient chemical/physical water quality monitoring from 2012 through 2014. None of the 36 samples collected during the 2012-2014 assessment period at the IDNR ambient monthly station violated Class B(WW1) water quality criteria for ammonia, pH, dissolved oxygen, chloride, sulfate, or temperature.

This evaluated biological assessment was based on data collected in 2012 and 2013 as part of the IDNR/SHL large river sampling project. A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa collected in the stream sampling reach. The biological metrics were combined to make a benthic macroinvertebrate index (BMIBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2012 BMIBI scores were 53 (fair) and 59 (good).  The 2013 BMIBI scores were 43 (fair) and 57 (good). The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008. The BMIBI BIC for this ecoregion is 51. This assessment is considered evaluated because the drainage area (988 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site passed the BMIBI BIC (3/4), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the site used for the assessment doesn’t fall in the calibrated watershed size.

Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this stream segment.

Monitoring and Methods
Assessment Key Dates
8/8/2012 Biological Monitoring
9/6/2013 Biological Monitoring
1/5/2012 Fixed Monitoring Start Date
12/3/2014 Fixed Monitoring End Date
230 Fixed station physical/chemical (conventional plus toxic pollutants)
315 Regional reference site approach
320 Benthic macroinvertebrate surveys
420 Water column surveys (e.g. fecal coliform)