Assessment Comments

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses were assessed as "fully supported / threatened.   Fish consumption uses remain "fully supported."  EXPLANATION:  The assessment of support of the Class B(WW) uses is based (1) on results of DNR monthly water quality monitoring conducted on Cedar Creek near Oakland Mills during the 1998-1999 biennial period and (2) on results of pesticide monitoring conducted from April 1996 to August 1998 by USGS as part of the National Water Quality Assessment Program (NAWQA) (eastern Iowa river basins study unit, station 05473400).   None of the 24 samples collected during the 1998-1999 biennial period at the DNR monthly station violated Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen; no violations occurred in the two samples analyzed for toxic metals.   Although these results suggest "full support" of the Class B(WW) uses, results of the USGS/NAWQA pesticide monitoring suggest that these uses be assessed as "fully supported / threatened."  One of 29 samples analyzed for pesticides contained chlorpyrifos above the Class B(WW) chronic criterion of 0.041 ug/l).   This sample was collected on June 17, 1996, and contained 0.0446 ug/l of chlorpyrifos).   According to U.S.  EPA guidelines for Section 305(b) reporting (U.S.  EPA 1997b, page 3-18), this one violation of a toxic contaminant does not suggest an impairment of the aquatic life uses.   Based on DNR's assessment methodology for Section 305(b) reporting, however, this violation suggests that the Class B(WW) aquatic life uses should be assessed as "fully supported/threatened."  Support of the fish consumption uses remains "fully supported" based on results from USGS/NAWQA fish tissue monitoring near Oakland Mills in September 1995 that showed very low levels of organochlorine contaminants (see assessment developed for the 1998 report).