Yellow River IA 01-YEL-434

[Note:  A TMDL for the bacterial impairment for streams in the Yellow River basin was prepared by Iowa DNR in 2012 and approved by U.S. EPA in 2013.  Due to completion of the TMDL, the Integrated Report category for the Class A1 recreational uses is changed from 5a (impaired; TMDL needed) to 4a (impaired; TMDL approved).]

The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" due to violations of Iowa’s water quality criteria for indicator bacteria.  The geometric means of indicator bacteria (E. coli) in the 24 monthly samples collected during the recreational seasons of 2012 through 2014 at IDNR-UHL station 10030002 near Volney were as follows:  the 2012 geometric mean was 87 orgs/100 ml, the 2013 geometric mean was 142 orgs/100 ml, and the 2014 geometric mean was 188 orgs/100 ml.  The 2013 and 2014 geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml; the 2012 geometric mean was well-below the Class A1 criterion.  Five of the 24 samples (21%) 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 both chemical/physical monitoring and biological sampling.  Results of monthly chemical/physical monitoring from the IDNR ambient station near Volney from 2012 through 2014 showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, ammonia, temperature, chloride, or sulfate in the 36 monthly samples collected from 2012-2014. 

In addition to chemical/physical monitoring, the assessment of aquatic life uses was also based on biological data collected in 2004 and 2012 as part of the IDNR/SHL stream biocriteria project.  A series of biological metrics which 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 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 2004 FIBI score was 65 (good) and the BMIBI score was 72 (good).  The 2012 FIBI score was 68 (good) and the BMIBI score was 81 (excellent).  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 biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.  The FIBI BIC for this ecoregion is 52 and the BMIBI BIC for this ecoregion is 61.  This segment passed the FIBI and BMIBI BICs 2/2 times in the last 11 years. 

This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology.  IDNR now requires a segment have two or more biological samples collected from the segment in multiple years over a recent five-year period to be considered “monitored”.  This segment had multiple samples collected in the previous 11 years (2004-2014); however, the multiple samples were not collected during a five-year period.

The fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this river reach.