Assessment Comments
Assessment is based on results of: (1) IDNR/SHL monthly ambient water quality monitoring conducted on the Yellow River near Volney during the 2010-2012 assessment period, (2) monitoring at IDNR TMDL station “Yellow River main stem site 3 in 2009, (3) results of fixed station water quality monitoring conducted at station YL01.5M from 2004 through 2006 by IDNR staff of the Upper Mississippi River "Long-Term Resource Monitoring Program (LTRMP) at Bellevue, IA., and (4) IDNR/SHL biological sampling conducted in 2004 and 2012.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" (IR 4a) due to high levels of indicator bacteria that violate state water quality standards. The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" (IR 2a) based on results of (1) biological sampling in 2004 and 2012 and on results of ambient chemical/physical water quality monitoring from 2010-2012. Fish consumption uses remain “not assessed” (IR 3a) due to the lack of fish contaminant monitoring in this river reach. The sources of data used for this assessment include (1) results of IDNR/SHL monthly ambient water quality monitoring conducted on the Yellow River near Volney (station 10030002) during the 2010-2012 assessment period, (2) results of monitoring at IDNR TMDL station “Yellow River main stem site 3 (station 11030002) from July to September 2009, (3) results of fixed station water quality monitoring conducted at station YL01.5M from 2004 through 2006 by IDNR staff of the Upper Mississippi River "Long-Term Resource Monitoring Program (LTRMP) at Bellevue, IA., and (4) IDNR/SHL biological sampling conducted in 2004 and 2012.
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 (see http://www.iowadnr.gov/Environment/WaterQuality/WatershedImprovement/WatershedResearchData/WaterImprovementPlans/PublicMeetingsPlans.aspx). 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).
EXPLANATION: 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 2010 through 2012 at IDNR-UHL station 10030002 near Volney were as follows: the 2010 geometric mean was 304 orgs/100 ml, the 2011 geometric mean was 78 orgs/100 ml, and the 2012 geometric mean was 87 orgs/100 ml. Only the 2010 geometric mean exceeds the Class A1 criterion of 126 orgs/100 ml; the 2011 and 2012 geometric means are well-below the Class A1 criterion. Four of the 24 samples (17%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. At IDNR-UHL TMDL station 11030002 near Volney, the geometric mean of indicator bacteria (E. coli) in the 14 samples collected during the recreational season of 2009 was 1,799 orgs/100 ml. Ten of the 38 samples (71%) from this station exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. This geometric mean is considerably higher than that seen during the 2010-12 period. 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 2010 through 2012 showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, ammonia, chloride, or sulfate in the 36 monthly samples collected from 2010-12. Similarly, results of monitoring in 2009 and IDNR TMDL station 11030002 near Volney show no violations of these parameters in the approximately 10 samples collection.
Results of LTRMP chemical/physical monitoring from 2004 through 2006 near the mouth of the Yellow River also suggest “full support” of the Class B(WW1) (aquatic life) uses. Monitoring data from LTRMP station YL01.5M show no violations of the Class B(WW1) water quality criteria for dissolved oxygen or pH in the 29 samples collected from February 2004 through June 2006. None of the 28 samples analyzed during this period violated Class B(WW1) criteria for ammonia nitrogen. Note: Station YL01.5M was not monitored by LTRMP after 2006.
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 nine 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 five-year period to be considered “monitored”. This segment had multiple samples collected in the previous seven years (2004-2012); 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.
