Assessment Comments

Assessment is based on (1) 2002 biocriteria data from the Dorchester monthly site(evaluated): BM-IBI= 58 (good); (2) DNR monthly fixed monitoring station near Dorchester, and (3) EPA/IDNR fish tissue (RAFT) monitoring in 1998.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses are assessed as “partially supported” due to high levels of indicator bacteria.   The Class B(WW) aquatic life uses were assessed (evaluated) as "fully supported / threatened" based on results of IDNR UHL biological monitoring in 2002.   Fish consumption uses remain assessed as "fully supported" based on results of fish contaminant monitoring in 1998.   Sources of data for this assessment include (1) results of DNR monthly water quality monitoring conducted on the Upper Iowa River near Dorchester (station 10030001) during the period January 2000 through December 2002, (2) results of IDNR/UHL biological monitoring in 2002, and (3) results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring in 1998.  

EXPLANATION: The Class A (primary contact recreation) uses are assessed as "partially supported" due to high levels of indicator bacteria (fecal coliforms).   Of the 21 samples from this station analyzed for indicator bacteria (fecal coliforms) during recreational seasons of 2000, 2001, and 2002, five 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 and Fischer and Eash 1998).   For purposes of Section 305(b) assessments, 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 16 non-runoff-affected samples was 87 orgs/100 ml; this geometric mean is far below the Iowa water quality standard of 200 orgs/100 ml.   Three of the 16 samples, however, (19%) exceeded the EPA-recommended single-sample maximum value of 400 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are "partially supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b)  

The Class B(WW) aquatic life uses were assessed as "fully supported" due to the lack of violations of state water quality criteria for pH, dissolved oxygen, and ammonia-nitrogen in the 36 samples during the 2000-2002 period.   In addition, no violations of Class B(WW) chronic criteria occurred in the ten samples analyzed for pesticides during the period.  

Results of biological monitoring conducted in 2002 as part of the IDNR/UHL stream biocriteria project suggest a threat to full support of the aquatic life uses.   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 2002 Fish IBI score was unavailable and the BM-IBI score was 58 (good).  The aquatic life use support was assessed (evaluated) as fully supporting/threatened (=FS/T), based on a comparison of the BM-IBI score 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 remain assessed (monitored) as "fully supported" based on results of EPA/DNR fish tissue (RAFT) monitoring in 1998 near Dorchester.   This monitoring showed that levels of all contaminants in the composite samples fillets from channel catfish and smallmouth bass were less than ½ of the respective FDA action levels and DNR levels of concern.