Missouri River IA 06-WEM-1709

Assessment Comments

Assessment is based on (1) surveys of Nebraska fisheries biologists, (2) consultation with DNR staff, (3) ambient monitoring by Nebraska DEQ, and (4) results of USGS/ NASQAN monitoring at Omaha (I-80 bridge).

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses remained "not assessed."  The Class B(WW) aquatic life uses were assessed as "partially supported."  Class C (drinking water) uses were assessed as "fully supported."  Fish consumption uses remain "not assessed."  EXPLANATION:  The Class A (primary contact recreation) uses remained "not assessed" due to lack of data on levels of indicator bacteria in this river reach.   The assessments of support for the Class B(WW) and Class C uses were based on results of water quality monitoring conducted from October 1997 through September 1999 by the U.S.  Geological Survey at the National Stream Quality Accounting Network (NASQAN) station at Omaha (station 06610000).   The Class B(WW) uses were assessed as "partially supported" based (1) the assessments developed for the 1998 report indicating impairments due to habitat alterations and flow modifications (see above) and (2) results of USGS monitoring showing that two of 29 samples (7%) analyzed for dieldrin during the 1998-1999 biennial period exceeded the Class B(WW) chronic criterion of 0.0019 ug/l.   The sample collected on August 7, 1999, contained 0.007 ug/l and the sample collected on August 23, 1999, contained 0.101 ug/l of dieldrin.   According to U.S.  EPA guidelines for Section 305(b) reporting (U.S.  EPA 1997b, page 3-18), the two violations of the chronic criterion for dieldrin indicate that the aquatic life uses are only "partially supported."  Levels of conventional and toxic parameters (pH, dissolved oxygen, and ammonia-nitrogen) and pesticides other than dieldrin (for example, chlorpyrifos, lindane, and parathion) were all below Class B(WW) criteria in the 29 samples analyzed during the biennial period.   Similarly, levels of toxic metals (for example, cadmium, chromium, and copper) were all below the respective Class B(WW) chronic criteria in the 19 samples analyzed.   Class C (drinking water) uses were assessed as "fully supported" due to the lack of violations of Class C criteria at the USGS station.   Levels of nitrate, atrazine, alachlor, cyanazine and toxic metals were well below their respective Class C criteria, MCLs and/or MCLGs in the 29 samples analyzed during the biennial period.   Fish consumption uses were "not assessed" due to the lack of fish tissue monitoring in this reach of the Missouri River.