Iowa DNR

Water Quality Assessments

Impaired Waters List

Wolf Creek IA 02-CED-530

mouth (S29, T87N, R11W, Black Hawk Co.) to confluence with Twelvemile Cr. in S19, T86N, R13W, Tama Co.

Assessment Cycle
Release Status
Release Period
2012 - 2014
8/16/2016 9:15:50 AM
Overall IR Category
5 - Water is impaired or threatened and a TMDL is needed.
Last Updated
12/1/2016 8:25:50 AM
Use Support
Class A1
Primary contact
Partially Supporting
Bacteria: Indicator Bacteria, E. coli
Impairment Code
5p - Impairment occurs on a waterbody with a presumptive A1 or B(WW1) use.
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 presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" (IR 5p) due to levels of indicator bacteria that violate state water quality criteria.  The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" (IR 2a) based on results of ambient water quality monitoring conducted from 2012 through 2014 and based on results of biological sampling conducted in 2004.  Fish consumption uses remain “not assessed” (IR 3a) due to the lack of recent fish contaminant monitoring in this assessment segment.  The primary sources of data for this are (1) the results of IDNR/SHL monthly ambient water quality monitoring conducted on Wolf Creek near LaPorte City (STORET station 10070002) during the 2012-2014 assessment period, (2) IDNR/SHL REMAP biological sampling conducted in 2004 near LaPorte City, and (3) USGS monitoring at station 05464220 near Dysart from September 2012 to September 2013. 

Assessment Explanation

The presumptive Class A1 uses are assessed as "partially supported" based on results of ambient monthly monitoring for indicator bacteria (E. coli).  The geometric means of indicator bacteria (E. coli) in the 24 monthly samples collected during the recreational seasons of 2012 through 2014 at Iowa DNR ambient station 10070002 at La Porte City were as follows:  the 2012 geometric mean was 407 orgs/100 ml, the 2013 geometric mean was 364 orgs/100 ml, and the 2014 geometric mean was 200 orgs/100 ml.  All three geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml.  Fourteen of the 24 samples (58%) 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 remains assessed (evaluated) as “fully supporting” based on data collected in 2004 as part of the IDNR/SHL stream REMAP 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 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 2004 FIBI score was 45 (fair) and the BMIBI score was 50 (fair).  The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports.  The non-riffle site FIBI BIC for this ecoregion is 44 and the artificial substrate BMIBI BIC for this ecoregion is 52.  This site met the BMIBI BIC with the aid of the BMIBI UAV (uncertainty adjustment value applied to single samples) of 8 points.  The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.  This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years in a five year period.  Despite this change in assessment methodology and type, this aquatic life assessment still suggests that this waterbody is fully supporting its' aquatic life uses.  Also, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). 

Additionally, results from IDNR/SHL ambient monthly monitoring at the La Porte City station from 2012-2014 show no violations of Class B(WW1) water quality criteria in the 36 monthly samples analyzed for dissolved oxygen, pH, ammonia-nitrogen, temperature, chloride and sulfate.  Results of monitoring from 2012 to 2013 at the USGS station near Dysart were similar:  no violations of Class B(WW1) water quality criteria occurred in the 18 samples analyzed for ammonia, dissolved oxygen, pH and temperature or in the 13 samples analyzed for chloride and sulfate.  These results suggest “full support” of the Class B(WW1) aquatic life uses.

Fish consumption uses are remain “not assessed” due to the lack of recent fish contaminant monitoring in this river segment.  Previous assessments were based on results of fish contaminant monitoring conducted by USGS in 1995 as part of the NAWQA project.  These data are now considered too old (greater than 10 years) to accurately characterize current water quality conditions.

Monitoring and Methods
Assessment Key Dates
8/19/2004 Biological Monitoring
1/5/2012 Fixed Monitoring Start Date
11/4/2014 Fixed Monitoring End Date
220 Non-fixed station physical/chemical monitoring (conventional pollutant only)
230 Fixed station physical/chemical (conventional plus toxic pollutants)
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
420 Water column surveys (e.g. fecal coliform)
150 Monitoring data more than 5 years old