Iowa DNR
ADBNet

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
2012
Release Status
Final
Result Period
2008 - 2010
Designations
Class A1 Class B(WW-1) Class HH
Assessment Type
Monitored
Integrated Report
Category 5a
Legacy ADBCode
IA 04-RAC-0170_0
Overall Use Support
Not supporting
Aquatic Life Use Support
Fully
Fish Consumption
Not assessed
Primary Contact Recreation
Not supporting
Documentation
Assessment Comments

Assessment is based on results of IDNR/UHL ambient monthly monitoring during the 2008-2010 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.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008 and results of an Use Attainability Analysis, this segment is also now designated for Class A1 (primary contact recreation) uses.   This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria.   The Class B(WW1) aquatic life are assessed (monitored) as "fully supported” based on results of ambient chemical/physical water quality monitoring from 2008 through 2010.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment.   The source of data for this assessment is the results of IDNR/UHL ambient monthly monitoring during the 2008-2010 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.  

EXPLANATION:  The Class A1 uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E.  coli).   The geometric means of indicator bacteria (E.  coli) in the 22 samples collected during the recreational seasons of 2008 through 2010 at IDNR station 10250001 near Redfield were as follows:  the 2008 geometric mean was 652 orgs/100 ml, the 2009 geometric mean was 314 orgs/100 ml, and the 2010 geometric mean was 1,452 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Fourteen of the 22 samples (64%) 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 are "not supported" (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/UHL ambient water quality monitoring from 2008 through 2010.   None of the approximately 30 samples collected during the 2008-2010 assessment period at the IDNR ambient monthly station violated Class B(WW1) water quality criteria for ammonia, pH, or dissolved oxygen.  

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
12/1/2010 Fixed Monitoring End Date
1/9/2008 Fixed Monitoring Start Date
Methods
230 Fixed station physical/chemical (conventional plus toxic pollutants)
420 Water column surveys (e.g. fecal coliform)
Monitoring Levels
Biological 0
Habitat 0
Physical Chemistry 3
Toxic 3
Pathogen Indicators 3
Other Health Indicators 0
Other Aquatic Life Indicators 0
# of Bio Sites 0
BioIntegrity N/A
Causes and Sources of Impairment
Causes Use Support Cause Magnitude Sources Source Magnitude
Pathogens Primary Contact Recreation Moderate
  • Source Unknown
  • Moderate