Assessment Comments

Assessment is based on results of IDNR monthy ambient water quality monitoring near Redfield from 2002-04.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life are assessed (monitored) as "fully supported” based on results of ambient chemical/physical water quality monitoring.   Fish consumption uses are "not assessed" due to the lack of fish contaminant monitoring in this river segment.   The source of data for this assessment is the results of IDNR/UHL ambient monthly monitoring during the 2002-2004 assessment period at STORET ambient monitoring station 10250001 (formerly station 429340) located near Redfield approximately 1 mile downriver from the confluence of Middle Raccoon and South Raccoon rivers.  

EXPLANATION:  The Class B(WW) aquatic life uses were assessed (monitored) as "fully supported”  based on results of IDNR/UHL ambient water quality monitoring from 2002 through 2004.   None of the 36 samples collected during the 2002-2004 assessment period at the IDNR monthly station violated Class B(WW) water quality criteria for pH or dissolved oxygen; no violations occurred in the ten samples analyzed for toxic metals or in the seven samples analyzed for pesticides and other toxic organic compounds.   One of the 36 samples analyzed, however, exceeded the Class B(WW) criterion for ammonia-nitrogen.   The sample collected on April 3, 2002, contained a ammonia nitrogen at 1.4 mg/l, thus exceeding state Class B(WW) criteria.   According to U.S.  EPA guidelines for Section 305(b) reporting (U.S.  EPA 1997b, page 3-18), this single violation of chronic criteria for ammonia does not suggest an impairment of aquatic life uses.   These guidelines state that uses are “fully supported” if chronic criteria for a toxic pollutant (for example, ammonia) are exceeded in up to one sample from an dataset based on monthly monitoring.   Thus, these results suggest that the Class B(WW) aquatic life uses of this river segment should be assessed as “fully supported”.  

Fish consumption uses were "not assessed" due to the lack of recent fish contaminant monitoring in this stream segment.