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

No violations of Class B(WW) WQ criteria for either conventional or toxic contaminants in the 24 sampled collected during the October 1995-September 1997 period; thus, assess support of the Class B(WW) aquatic life uses as FST.   Because data from RAFT fish contaminant monitoring are more than five years old, and because results from the 1997 RAFT status sampling are not yet available, did not use RAFT data for assess fish consumption uses.*  Results of fish tissue monitorng conducted in Sept.  1995 at Charles City for the USGS National Water Quality Assessment (NAWQA) program, however, were used to assess support of the fish consumption uses.   The whole- fish composite sample of carp was analyzed for several organochlorine compounds including chlordane, dieldrin, DDT, and PCBs.   Levels of all contaminants in the whole-fish sample were less than 1/2 of the respective FDA action levels, thus suggesting full support (FS) of fish consumption uses.  Additional monitoring is needed to determine the status of the aquatic communities and habitats in this river reach.  

*Data for the 1997 RAFT fish contaminant monitoring were received in August 1998.   Based on results of levels of contaminants in composite samples of fillets from channel catfish and smallmouth bass, continue to assess support of the fish consumption uses as FS due to all contaminant levels less than 1/2 of the respective FDA action levels.   Relative to other RAFT sites, very few contaminants were detected in these samples.   The level of mercury in the composite sample of smallmouth bass fillets (0.414 ppm), however, approached 1/2 of the action level for mercury (0.500 ppm).   Levels of mercury in fish from this location have historically been relatively high compared to other locations in Iowa (see page 2-47 of the 1986 305(b) report:  Water Quality in Iowa During 1984 and 1985).  The level of merucry in the 1997 RAFT sample is, however, consistent with results of previous monitoring.