Des Moines River IA 04-UDM-1212

Assessment Comments

Basis for Assessment

Assess support of the Class B(WW) aquatic life uses as FST:  the only violation of Class B(WW) WQ criteria for conventional or toxic pollutants were for two toxic metals: copper & mercury.   One of 12 samples collected from Oct 94 to Sep 97 exceeded the chronic WQ criterion for copper (sample was collected on Oct 11, 1994).   Ten of 11 samples collected during this period exceeded the Class B(WW) chronic criterion for mercury.  Due to (1) problems with analysis of mercury in water (see pages 3-58 and 3-99 to 3-100 of Iowa's 1996 Section 305(b) report), and (2) historical lack of high levels of mercury in fish tissue samples from this reach of river, data for mercury in water were not used to develop the assessment of support of the Class B(WW) aquatic life uses.   According to Section 305(b) assessment guidelines, the single violation of the WQ criterion for copper does not suggest a WQ imparment.   Thus, the Class B(WW) aquatic life uses were assessed as FST with the threat from high levels of toxic metals (copper).   Fish contaminant monitoring conducted in this reach by ISU during 1996 & 97 showed that levels of pesticides in composite samples of 3-yr old whole-fish carp were well below 1/2 of the respective FDA action levels; thus, fish consumption uses were assessed as FS.  This reach of the Des Moines River remains extremely popular for fishing.