Iowa DNR
ADBNet

Water Quality Assessments

Impaired Waters List

North Raccoon River IA 04-RAC-1132

from confluence with Indian Cr. (S24 T87N R36W Sac Co.) to confluence with Cedar Cr. in S25 T88N R36W Sac Co.

Assessment Cycle
2006
Result Period
2002 - 2004
Designations
Class A Class B(WW)
Assessment Methodology
Assessment Type
Monitored
Integrated Report
Category 5a
Legacy ADBCode
IA 04-RAC-0040_6
Overall Use Support
Not supporting
Aquatic Life Use Support
Partial
Fish Consumption
Not assessed
Primary Contact Recreation
Not supporting
Documentation
Assessment Comments

Assessment is based on results of (1) IDNR/UHL monthly ambient water quality monitoring downstream from Sac City from 2002-04 and evaluated IDNR/UHL biological (biocriteria) monitoring conducted in 2001.

Basis for Assessment

Note:  This assessment is also used for the adjacent downstream segment (IA 04-RAC-0040-5).

SUMMARY:  The Class A (primary contact recreation) uses are assessed (monitored) as "not supported" due to levels of indicator bacteria (E.  coli) that violate state water quality standards.   The Class B(WW) aquatic life uses are assessed (evaluated) as "partially supporting" based on results of IDNR/UHL biological (biocriteria) monitoring in 2001.   The fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.   The sources of data for this assessment include (1) the results from the IDNR/UHL ambient monthly monitoring station downstream from Sac City in Sac County (STORET station 10810001 (formerly station 423014)) located approximately 5 miles south of Sac City from 2002-2004 and (2) results of IDNR/UHL biological (biocriteria) monitoring in 2001.

EXPLANATION:  The Class A uses are assessed as "not supported" due to levels of indicator bacteria (E.  coli) that exceed state water quality criteria.   Due to recent changes in Iowa’s Water Quality Standards, Iowa’s 2006 assessment methodology for indicator bacteria has changed.   Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses:  the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff."  Due to a change in the Standards in July 2003, E.  coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E.  coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.”  Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E.  coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of the 2006 Section 305(b) assessments and Section 303(d) listings.  

The geometric mean level of indicator bacteria (E.  coli) in the 37 samples collected during the recreational seasons of 2002, 2003, and 2004 (294 orgs/100ml) exceeded the Iowa Class A water quality criterion of 126 orgs/100ml.   In addition, 15 of the 37 samples (41%), however, exceeded Iowa’s single-sample maximum value of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, and according to IDNR’s assessment/listing methodology, if the geometric mean 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 3-35of U.S.  EPA 1997b).  

The Class B(WW) aquatic life uses were also assessed using biological data collected in 2001 as part of the ambient water monitoring project and the DNR/UHL stream biocriteria project.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data.   The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach.   The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2001 evaluated FIBI score was 54 (good) and 2001 evaluated BMIBI score was 50 (fair), respectively.  The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   The non-riffle FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62.   This assessment is considered evaluated because the drainage area (712.9 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 FIBI BIC and failed the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size.   The results of this sampling thus do not meet IDNR guidelines for developing a “monitored” assessment of support of the aquatic life uses that is appropriate to support addition of this waterbody to Iowa's Section 303(d) list.  

Results of IDNR/UHL ambient chemical/physical water quality monitoring at the Sac City station during the 2002-2004 assessment period, however, suggest relatively good water quality in this river segment.   Results of this monitoring show no violations of Class B(WW) (aquatic life) water quality criteria in the approximately 45 samples analyzed for dissolved oxygen, ammonia, and pH, in the 14 samples analyzed for toxic metals, or in the 15 samples analyzed for pesticides and other toxic organic compounds.  

Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.   The most recent fish contaminant monitoring was conducted in 1993 as part of the U.S.  EPA/IDNR RAFT program.   These data are too old to accurately characterize current contaminant levels.

Monitoring and Methods
Assessment Key Dates
12/13/2004 Fixed Monitoring End Date
1/9/2002 Fixed Monitoring Start Date
10/3/2001 Biological Monitoring
Methods
220 Non-fixed station physical/chemical monitoring (conventional pollutant only)
315 Regional reference site approach
320 Benthic macroinvertebrate surveys
330 Fish surveys
380 Quan. measurements of instream parms-- channel morphology-- floodplain-- 1-2 seasons-- by prof
230 Fixed station physical/chemical (conventional plus toxic pollutants)
Monitoring Levels
Biological 4
Habitat 4
Physical Chemistry 3
Toxic 3
Pathogen Indicators 3
Other Health Indicators 0
Other Aquatic Life Indicators 0
# of Bio Sites 1
BioIntegrity Fair
Causes and Sources of Impairment
Causes Use Support Cause Magnitude Sources Source Magnitude
Pathogens Primary Contact Recreation High
  • Source Unknown
  • Moderate
Cause Unknown Aquatic Life Support Slight
  • Source Unknown
  • Slight