Assessment Comments
Assessment is based on: (1) results of IDNR/UHL monthly ambient water quality monitoring conducted on the Yellow River near Volney (station 10030002) during the 2006-2008 assessment period, (2) 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 (3) IDNR/UHL biological monitoring conducted in 2002 and 2004.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" 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" based on results of (1) biological monitoring in 2002 and 2004 and on results of ambient chemical/physical water quality monitoring from 2006-2008. Fish consumption uses remain “not assessed” 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/UHL monthly ambient water quality monitoring conducted on the Yellow River near Volney (station 10030002) during the 2006-2008 assessment period, (2) 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 (3) IDNR/UHL biological monitoring conducted in 2002 and 2004.
EXPLANATION: The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric mean of E. coli in the 39 samples collected from the IDNR/UHL ambient monitoring station near Volney (10030002) during the recreational seasons of 2006 through 2008 was 306 orgs/100 ml; 21 of the 39 samples (54%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. This geometric mean exceeds the state water quality criterion of 126 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 level 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(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of both chemical/physical monitoring and biological monitoring. Results of monthly-plus chemical/physical monitoring from the IDNR ambient station near Volney from 2006 through 2008 showed no violations of Class B(WW1) water quality criteria for dissolved oxygen in the 56 samples collected or for pH, or ammonia in the 32 samples collected. Monitoring results for dissolved oxygen are in contrast to those from the previous (2004-06) assessment period when ten of 89 samples collected violated the Class B(WW1) criterion for dissolved oxygen. All of these violations occurred from June to September 2005; the violations ranged from 3.2 to 4.8 mg/l. The lack of violations for dissolved oxygen during the 2006-08 assessment period suggests that the low levels that occurred from June to September of 2005 (which did not indicate impairment of the Class B(WW1) uses) were a temporary/transient occurrence. Neither of the two samples analyzed for toxic metals violated the respective chronic aquatic life criteria.
Similarly, results of LTRMP chemical/physical monitoring near the mouth of the Yellow River from 2004 through 2006 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 2002 and 2004 as part of the IDNR/UHL stream biocriteria and REMAP projects. 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 biocriteria FIBI score was 65 (good) and the BMIBI score was 72 (good). The 2002 REMAP FIBI score was 54 (good) and the BMIBI score was 63 (good). 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 1994-2004. 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 seven 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 between 2004 and 2008 to be considered “monitored”. This segment had multiple samples collected in the previous seven years (2002-2008); however, the multiple samples were not collected during 2004-2008.
The fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this river reach. Levels of all toxic metals in the two samples analyzed, however, were below the respective human health (fish) criteria.
