Des Moines River IA 04-UDM-1211

Assessment Comments

Basis for Assessment

Class A primary contact recreation uses were assessed as FS:  none of the 18 samples collected during summers of 1996 & 97 exceeded the Class A WQ criterion of 200 fecal coliforms/100 ml (geometric mean= 11 orgs/100 ml; max= 70 orgs/ 100 ml).   The only violations of Class B(WW) WQ criteria for conventional or toxic pollutants were for copper & mercury.   One of 12 samples from Oct 94 to Sep 97 exceeded the Class B(WW) chronic criterion for copper.   Ten of 11 samples collected during this period exceeded the Class B(WW) chronic criterion for mercury.   Due to (1) problems with analysis of Hg in water (see pages 3-58 & 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, data for mercury were not used for this assessment.   Single violation for copper does not suggest impairment; thus Class B(WW) uses assessed as FST.   Fish contam.  mon by ISU in 96 & 97 shows low level of pesticides well below 1/2 of FDA action levels; thus, fish consumption uses assessed as FS.   Class C drinking water uses assessed as FST: 3 of 67 samples coll.  between Oct 94 & Sep 97 exceeded the MCL for nitrate (4.5% viol; mean=6.07 & median=5.93 mg/l).   Viols from Apr-Jun 1995.  No other violations of Class C WQ criteria.