Upper Iowa River IA 01-UIA-236

Assessment Comments

Assessment is based on DNR monthly fixed monitoring station near Dorchester and EPA/IDNR fish tissue (RAFT) monitoring in 1998.

Basis for Assessment

SUMMARY:  Class A (primary contact recreation) uses remain assessed as "fully supported."  Class B(WW) aquatic life uses assessed as "fully supported."  Fish consumption uses were assessed as "fully supported."  EXPLANATION:  The assessments of support of beneficial uses are based on results of DNR monthly water quality monitoring conducted on the Upper Iowa River near Dorchester during the 1998-1999 biennial period.   The Class A (primary contact recreation) uses remain assessed as "fully supported."  Of the 14 samples from this station analyzed for indicator bacteria (fecal coliforms) during summers of 1998 and 1999, 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).   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 nine non-runoff-affected samples was 74 orgs/100 ml; one of the nine samples (11%) exceeded the EPA-recommended single-sample maximum value of 400 orgs/100 ml.   The geometric mean (74 orgs/100 ml) is well below the state water quality criterion of 200 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 only "partially supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b)  Due, however, to (1) the lack of sufficient data points for developing a "monitored" assessment (according to DNR's 305(b) assessment methodology, "monitored" assessments require at least 10 non-runoff-affected samples), and (2)  the relatively low geometric mean, the Class A uses of this river reach were assessed as "fully supporting" for the 1998-1999 biennial period.   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 24 samples during the 1998-1999 biennial period.   In addition, no violations of Class B(WW) chronic criteria occurred in the one sample analyzed for toxic metals during the biennial period.   The fish consumption uses were assessed 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.