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
2016
Release Status
Final
Data Collection Period
Overall IR Category
4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trend
Unknown
Created
10/4/2016 8:15:04 AM
Updated
11/4/2016 9:59:33 AM
Assessment conducted in accordance with Iowa's 2016 IR methodology
Use Support
Class A1
Partially Supported
Bacteria: Indicator Bacteria- E. coli
Support Level
Partially Supported
Impairment Code
4a - Pollutant-caused impairment. TMDL has been completed.
Cause Magnitude
Slight
Status
Continuing
Source
Unknown: Source Unknown
Source Confidence
N/A
Cycle Added
2008
Impairment Rationale
Geometric mean criterion exceeded
Data Source
Ambient monitoring: Iowa DNR-rivers
Class BWW1
WINOFI
Biological: low aquatic macroinvertebrate IBI
Support Level
Water in Need of Further Investigation (WINOFI)
Impairment Code
3b-u - Use potentially biologically impaired based on uncalibrated IBI metrics.
Cause Magnitude
Moderate
Status
Continuing
Source
Unknown: Source Unknown
Source Confidence
Low
Cycle Added
2002
Impairment Rationale
Low Biotic Index
Data Source
Biological monitoring: Iowa DNR WQMA
Class HH
Not Assessed
General Use
Not Assessed
Impairment Delistings
No delistings for this assessment cycle.
Documentation
Assessment Summary

The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" (IR 4a) due to levels of indicator bacteria (E. coli) that slightly violate state water quality standards. The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supporting" (IR 3b-u) based on results of IDNR/SHL biological sampling in 2005 and 2013. The fish consumption uses remain not assessed. The sources of data for this assessment include (1) the results from the IDNR/SHL 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 2012-2014, (2) results of USGS ambient monitoring near Sac City at station 05482300 from August 2012 through August 2013, and (3) results of IDNR/SHL biological sampling conducted in 2001, 2005 and 2013.

Assessment Explanation

[Note 1: This assessment is also used, in part (except for the assessment of fish consumption uses) for the adjacent downstream segment (IA 04-RAC-0040-5).]

[Note 2: A TMDL for pathogen indicator (E. coli) impairments in the Raccoon River basin was prepared by IDNR and approved by EPA in June 2008. Because this TMDL covers the primary Section 303(d) impairment identified for the 2006 assessment/listing cycle, this waterbody was moved from IR Category 5a from the 2006 assessment/listing cycle to IR Category 4a (impaired; TMDL approved) for the 2008 cycle. This waterbody remains in IR Category 4a for the current cycle.]

The Class A1 uses are assessed (monitored) as "partially supported" due to levels of indicator bacteria (E. coli) that exceed state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 25 samples collected during the recreational seasons of 2012 through 2014 at IDNR station 10810001 near (downstream from) Sac City were as follows: the 2012 geometric mean was 128 orgs/100 ml, the 2013 geometric mean was 169 orgs/100 ml, and the 2014 geometric mean was 292 orgs/100 ml. All three geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml. Eight of the 24 samples (33%) 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.”  Note:  monitoring for indicator bacteria was not conducted at the USGS monitoring station during the 2012-2014 monitoring period.

The Class B(WW1) aquatic life uses are assessed (evaluated) as “partially supporting” based on biological data collected in 2001, 2012 and 2013 by the IDNR/SHL stream biological monitoring 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 FIBI score was 57 (good). The 2012 BMIBI score was 29 (poor) and the 2013 BMIBI score was 47 (fair). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC is 62. This segment passed the FIBI BIC in 2001 and passed the BMIBI BIC 0/2 times in the last five years (2010-2014). This assessment is considered evaluated because the drainage area (709 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 the site used for the assessment 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. The assessment type for these waters will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to “monitored" (indicating an assessment with relatively high confidence). Such waters will be placed in either Category 2b or 3b of the IR and thus will be added to the state’s list of “waters in need of further investigation.”

Results of IDNR/SHL ambient chemical/physical water quality monitoring at the Sac City station during the 2012-2014 assessment period, however, suggest relatively good water quality in this river segment. Results of this monitoring show no violations of Class B(WW1) (aquatic life) water quality criteria in the 36 samples analyzed for ammonia, dissolved oxygen, temperature, chloride, and sulfate. Three of the 36 samples collected (8%) exceeded the Class A, B(WW1) criterion for pH. According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed state criteria for conventional parameters such as pH, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, however, the results from IDNR station 10810001 do not indicate that greater than 10% of the samples exceed either the Class B(WW1) criteria for pH. Similarly, results of monitoring at USGS station 05482300 near Sac City did not show violation of Class B(WW1) criteria in the approximately 12 samples analyzed for ammonia, chloride, dissolved oxygen, pH, sulfate, and temperature.  Thus, these results do not suggest impairment of the Class B(WW1) aquatic life uses.

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
9/10/2012 Biological Monitoring
8/12/2013 Biological Monitoring
10/3/2001 Biological Monitoring
1/9/2012 Fixed Monitoring Start Date
12/3/2014 Fixed Monitoring End Date
Methods
150 Monitoring data more than 5 years old
230 Fixed station physical/chemical (conventional plus toxic pollutants)
315 Regional reference site approach
320 Benthic macroinvertebrate surveys
330 Fish surveys
380 Quantitative physical habitat assessment
420 Indicator bacteria monitoring