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 2004-2006 assessment period, (2) results of monitoring for indicator bacteria at IDNR/UHL station 15030002 near Old Mission Road from May to November 2004, (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/UHL biological monitoring conducted in 2002 and 2004.

Basis for Assessment

SUMMARY:  The Class A1 (primary contact recreation) uses were 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 were 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 by two agencies from 2004-2006.   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 2004-2006 assessment period, (2) results of monitoring for indicator bacteria at IDNR/UHL station 15030002 near Old Mission Road from May to November 2004, (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/UHL biological monitoring conducted in 2002 and 2004.

EXPLANATION:  The Class A1 (primary contact recreation) uses were assessed (monitored) as "not supported" due to violations of Iowa’s water quality criteria for indicator bacteria.   Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed.   Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses:  the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff."  Due to a change in the Standards in July 2003, E.  coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E.  coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.”  Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E.  coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of the 2006 Section 305(b) assessments and Section 303(d) listings.  

The geometric mean of E.  coli in the 118 samples collected from the IDNR/UHL ambient monitoring station near Volney (10030002) was 190 orgs/100 ml; 47 of the 118 samples (40%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.   The geometric mean (190 orgs/100 ml) 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 geometric mean of E.  coli in the 25 samples collected from the IDNR/UHL monitoring station near Old Mission Road (15030002) was 463 orgs/100 ml., thus far exceeding the state water quality criterion of 126 orgs/100 ml.   Also, 12 of the 25 samples (48%) exceeded Iowa’s single-sample maximum criterion of 235 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 are "not supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).   Thus, the results of bacterial monitoring at both DNR/UHL monitoring stations (i.e., near Volney and near Old Mission Road) suggest that the Class A1 (primary contact recreation) should be assessed (monitored) as "not supported."

Due to the availability of weekly bacteria data for the IDNR/UHL ambient station at Volney (station 10030002) for the recreation seasons of 2004 and 2005, the thirty-day/five-sample geometric means were calculated for these two recreation seasons (in 2006, the sampling frequency at this monitoring station returned to monthly).   In the 2004 recreation season, 15 of the 26 thirty-day geometric means exceeded Iowa’s Class A1 criterion of 126 orgs/100 ml.   In the 2005 recreation season, 19 of the 34 geometric means exceeded the Class A1 criterion.   As noted above, U.S.  EPA guidelines for Section 305(b) reporting and the IDNR assessment/listing methodology state that a single geometric mean greater than the state criterion of 126 orgs/100 ml.  suggests that the Class A1 uses are “not supported.”  Thus, when assessed on the basis of thirty-day/5-sample geometric means, the data for indicator bacteria at this station also suggest nonsupport of the Class A1 uses.  

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 chemical/physical monitoring from the IDNR ambient station near Volney from 2004 through 2006 showed no violations of Class B(WW1) water quality criteria for pH (62 samples analyzed) or ammonia (61 samples analyzed).   Ten of 89 samples, however, 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.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), this violation frequency does not indicate impairment of aquatic life uses.   That is, based on IDNR’s assessment methodology, these results do not suggest that significantly more than 10 percent of the samples exceed Iowa’s dissolved oxygen criteria and thus do not suggest an impairment of the Class B(WW1) uses.   Despite the lack of impairment, the repeated occurrence of low levels of dissolved oxygen in summer 2005 is unusual for Iowa rivers and is thus cause for concern.   Of the ten samples analyzed for toxic metals at the DNR station near Volney, only one sample violated a Class B(WW1) criterion:  one of the ten samples analyzed for lead exceeded the Class B(WW1) criterion of 30 ug/l.   This violation occurred on July 6, 2004; the level of lead in the sample was 40 ug/l.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-18), however, one violation of a water quality criterion for a toxic pollutant in an abundant data set (at least 10 samples over at three-year period) does not indicate an impairment of aquatic life uses.  

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.  

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 FIBI average was 59.5 and the BMIBI average was 67.5.   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.

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