East Nishnabotna River IA 05-NSH-1414

Assessment Comments

Assessment is based on results of IDNR/UHL ambient water quality monitoring conducted in support of TMDL development from 2003-2004.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported" based on results of chemical/physical water quality monitoring.   Fish consumption uses remain “not assessed due to the lack of fish contaminant monitoring in this river reach.   This assessment is based on results of IDNR/UHL ambient monitoring conducted downstream from Shenandoah in support of TMDL development during the 2002-2004 assessment period (STORET station 10360002).

EXPLANATION:  This assessment is based on results of monitoring for conventional and toxic parameters conducted from July 2003 to October 2004 downstream from Shenandoah in support of TMDL development.   Results of ambient monitoring at the IDNR/UHL station showed no violations of Class B(WW) water quality criteria during the 2002-2004 assessment period for ammonia-nitrogen (maximum value = 0.64 mg/l) or for pH in the 18 samples collected.   One of the 18 samples (6%) analyzed for dissolved oxygen did violate the Iowa Water Quality criterion to protect Class B(WW) uses:  the sample collected on February 3, 2004 contained 3.8 mg/l of dissolved oxygen, thus violating the Iowa criterion of 5.0 mg/l.   According to U.S.  EPA guidelines (U.S.  EPA 1997b, page 3-17), however, a violation frequency of less than 10 % for conventional parameters such as dissolved oxygen suggest "full support" of aquatic life uses.   Thus, the percentages of violations of the dissolved oxygen criterion at this station (6%) does not suggest an impairment of the Class B(WW) aquatic life uses.   Levels of pesticides in the five samples analyzed, and levels of toxic metals in the six samples analyzed, were all below the respective Class B(WW) criteria.   Based on these data, the Class B(WW) aquatic life uses are assessed (monitored) as “fully supported”.  

Fish consumption uses remain “not assessed due to the lack of fish contaminant monitoring in this river reach.