Assessment Comments

Assessment is based on results from the DNR monthly water quality monitoring station at Hwy 59 near Shenandoah.

Basis for Assessment

SUMMARY:  Class B(WW) aquatic life uses were assessed as "fully supporting" and fish consumption uses were considered "not assessed."  EXPLANATION:  Class B(WW) aquatic life uses were assessed as "fully supporting" due to the lack of violations of Class B(WW) 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 monitoring station at the Highway 59 bridge north of Shenandoah (station 821008) during the 1998-1999 biennial period.   For the 1998 report, the Class B(WW) aquatic life uses were assessed as "fully supported" but "threatened" due to historical impacts of extensive channelization and other impacts of the riparian corridor of the East Nishnabotna River and due to other impacts in the riparian corridor (see above).   This assessment of "threatened," however, was strictly a "best professional judgement" and was not supported by field assessments of either habitat or the biological communities.   Until such assessments are conducted, the assessment of support of the Class B(WW) uses will be based only on results of the available information on chemical water quality monitoring and the comparisons of these results to the Iowa Water Quality Standards.   Thus, the Class B(WW) uses were assessed as "fully supporting" for the 2000 report.   Although this river reach is not designated for Class C (drinking water) uses, results of pesticide monitoring show no levels of atrazine in the 24 samples collected from October 1997 through September 1999 that exceeded the MCL of 3.0 ug/l (maximum:  1.6 ug/l).   Similarly, levels of nitrate in the 24 samples were all below the 10 mg/l MCL (maximum:  9.3 mg/l; mean:  6.1; standard deviation = 1.85 mg/l).   Fish consumption uses were considered "not assessed due to the lack of recent fish tissue monitoring in this river reach.   Although fish consumption uses were assessed for the 1996 and 1998 reports based on EPA/DNR fish tissue (RAFT) monitoring near Red Oak (see above), this monitoring was conducted well upstream from this waterbody segment.   Thus, the fish contaminant data from near Red Oak are of questionable use for characterizing fish contaminant levels in this assessment segment.