Assessment Comments

Assessment based on results of (1) 2002 DNR REMAP data: Fish IBI= 54 (good), BM-IBI= 62 (good); (2) 1998 DNR Biocriteria data: Fish IBI= 63 (good), BM-IBI= 67 (good), and (3) IDNR/UHL ambient monthly WQ monitoring at Volney from 2000-02.

Basis for Assessment

SUMMARY:  Class A (primary contact recreation) uses were assessed (monitored) as "not supported" due to high levels of indicator bacteria that violate state water quality standards.   Class B(WW) aquatic life uses were assessed as "fully supported/threatened" based on results of (1) IDNR/UHL biological monitoring in 1998 and 2002 and (2) results of IDNR/UHL ambient monitoring that show a single violation of the Class B(WW) water quality criteria for ammonia nitrogen.   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 2000-2002 assessment period and (2) IDNR/UHL biological monitoring conducted in 1998 and 2002.

EXPLANATION:  The Class A (primary contact recreation) uses were assessed (monitored) as "not supported" due to violations of Iowa’s water quality criteria for indicator bacteria.   Of the 21 samples from this station analyzed for indicator bacteria (fecal coliforms) during summers of 2000, 2001, and 2002, three samples were collected during conditions of high river flow.   These high flows resulted in monitoring at river discharges that exceeded the long-term monthly average flow plus one standard deviation of this average (flow statistics from Fischer et al.  1990).   For purposes of Section 305(b) assessments only, DNR uses the long-term average monthly flow plus one standard deviation of this average to identify river flows that are materially affected by surface runoff.   According to the Iowa Water Quality Standards (IAC 1990:8), the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) does not apply "when the waters are materially affected by surface runoff."  The geometric mean of fecal coliform bacteria in the 18 non-runoff-affected samples was 223 orgs/100 ml; six of the 18samples (33%) exceeded the EPA-recommended single-sample maximum value of 400 orgs/100 ml.   The geometric mean (223 orgs/100 ml) is slightly above the state water quality criterion of 200 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, if the geometric mean is greater than 200 orgs/100ml the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).   Thus, the Class A (primary contact recreation) uses were assessed as "not supported" for the 2000-2002 assessment period.  

Class B(WW) aquatic life uses were assessed as "fully supported/threatened [no declining trend]" based on results of both chemical/physical monitoring and on results of biological monitoring.   The occurrence of one violation of Iowa’s chronic water quality criterion for ammonia-nitrogen in one of the 36 samples collected during the assessment period suggests that the Class B(WW) uses are “fully supported / threatened.”  This violation occurred on March 21, 2000; the level of ammonia in the sample was 1.4 mg/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) set does not indicate an impairment of aquatic life uses; according to IDNR assessment methodology, however, this one violation does indicate a threat to full support of the aquatic life uses.   No violations of state water quality criteria occurred for pH, or dissolved oxygen in the 36 samples during the 2000-2002 assessment period.   In addition, no violations of Class B(WW) chronic criteria occurred in the ten samples analyzed for pesticides during the assessment period.  

In addition to chemical/physical monitoring, the assessment of aquatic life uses was also based on biological data collected in 1998 and 2002 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 biocriteria 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 (F-IBI) and a benthic macroinvertebrate index (BM-IBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 1998 biocriteria Fish IBI score was 63 (good) and the BM-IBI score was 67 (good).   The 2002 REMAP Fish IBI score was 54 (good) and the BM-IBI score was 62 (good).   The aquatic life use support was assessed as fully supporting/threatened (=FS/T), based on a comparison of the F-IBI and BM-IBI scores from the 1998 and 2002 samplings with biological assessment criteria established for previous Section 305(b) reports.  The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.      

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