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."  The fish consumption uses remain assessed as "fully supporting."  The primary sources of data for this assessment are (1) results of IDNR ambient monthly monitoring approximately 4 miles southeast of Charles City and (2) results of U.S.  EPA/IDNR fish tissue (RAFT) monitoring 4 miles southeast of Charles City in 1997.   EXPLANATION:  The Class B(WW) aquatic life uses were assessed as "fully supporting" due to the lack of violations of water quality criteria in (1) the 24 samples analyzed for conventional and toxic parameters (dissolved oxygen and ammonia-nitrogen) and (2) the four samples analyzed for toxic metals and toxic organic compounds at the IDNR monthly monitoring station during the 2000-2001 biennial period.   These results suggest full support of the Class B(WW) uses.   The levels of pH in the sample collected on May 1, 2000, was 9.2 units and thus violated the Class B(WW) criterion of 9.0 pH units.   This violation occurred on a day when dissolved oxygen levels were relatively high (15.4 mg/l) and were at 140% of saturation.   These conditions suggest that high levels of primary productivity resulted in the high level of pH.   Because this violation is more related to natural conditions than to pollution, the occurrence of high levels of pH in this river segment is not seen as a water quality impairment.   This station 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 (see assessment for the 2000 report above).   Results of this monitoring showed that one of 27 samples violated the Class B(WW) chronic water quality criterion for DDE.   This violation led to the assessment of the Class B(WW) uses as "fully supported/threatened" for the 2000 reporting cycle.   IDNR monitoring during the 2000-2001 biennial period, however, showed no violations of the Class B(WW) water quality criterion for DDE in the 6 samples analyzed.   Thus, the assessment of the Class B(WW) uses was revised to "fully supported" (not threatened) for the 2002 reporting cycle.   Fish consumption uses remain assessed as "fully supported" based on results of EPA/DNR fish tissue (RAFT) monitoring southeast of Charles City in 1997.   Results of this sampling showed that levels of all contaminants were below ½ of the respective FDA action levels and DNR levels of concern (see assessments for the 1998 and 2000 reports).