Assessment Comments

Assessment is based on results of the following monitoring downstream from Charles City (1) IDNR monthly ambient monitoring and (2) fish tissue (RAFT) monitoring.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses are assessed as "fully supporting/threatened;" the fish consumption uses remain assessed as "fully supporting."  EXPLANATION:  The Class B(WW) aquatic life uses were assessed as "fully supporting / threatened" due to the lack of violations of water quality criteria in (1) the 24 samples analyzed for conventional and toxic parameters (dissolved oxygen, pH, and ammonia-nitrogen) and (2) the one sample analyzed for toxic metals at the DNR monthly monitoring station on the Cedar River at Carville during the 1998-1999 biennial period.   These results suggest full support of the Class B(WW) uses.   This station, however, was monitored for toxic organic compounds and pesticides from March 1996 to September 1998 as part of the USGS National Water Quality Assessment (NAWQA) program in the eastern Iowa river basins study unit (station 05457750).   Results of this monitoring showed that one of 27 samples violated the Class B(WW) chronic water quality criterion for DDE.   According to U.S.  EPA guidelines for Section 305(b) reporting (U.S.  EPA 1997b, page 3-18), this one violation 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."  Fish consumption uses remain assessed based on results of USGS / NAWQA fish contaminant monitoring near Carville in September 1995 and on results of EPA/DNR fish tissue (RAFT) monitoring in 1997.   Both samplings showed that levels of all contaminants were below ½ of the respective FDA action levels and DNR levels of concern (see assessment for the 1998 report).