Assessment Comments
Assessment based on results of (1) 1998 DNR Biocriteria sampling: Fish IBI= 63(good), BM-IBI= 67(good), (2) DNR monthly WQ monitoring at Volney, and (3) WQ monitoring at Sny Magill / Bloody run project site near mouth.
Basis for Assessment
SUMMARY: Class A (primary contact recreation) uses were assessed as "not supported." Class B(WW) aquatic life uses were assessed as "fully supported/threatened." Fish consumption uses remain were not assessed. The sources of data used for this assessment include results of DNR monthly ambient water quality monitoring conducted on the Yellow River near Volney during the 2000-2001 biennial period (October 1999 through September 2001). EXPLANATION: The Class A (primary contact recreation) uses were assessed as "not supported." Of the 15 samples from this station analyzed for indicator bacteria (fecal coliforms) during summers of 2000 and 2001, 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 twelve non-runoff-affected samples was 259 orgs/100 ml; four of the twelve samples (33%) exceeded the EPA-recommended single-sample maximum value of 400 orgs/100 ml. The geometric mean (259 orgs/100 ml) is 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 crecation 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 2000-2001 biennial period. Class B(WW) aquatic life uses were assessed as "fully supported/threatened [no declining trend]" due to the occurrence of one violation of the chronic water quality criterion for ammonia-nitrogen in one of the 24 samples collected during the biennial period (this violation occurred on March 21, 2000). 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. No violations of state water quality criteria occurred for pH, or dissolved oxygen in the 24 samples during the 2000-2001 biennial period. In addition, no violations of Class B(WW) chronic criteria occurred in the four samples analyzed for toxic metals or in the seven samples analyzed for pesticides during the biennial period. The fish consumption uses were not assessed due to the lack of fish contaminant monitoring in this river reach.
