Assessment Comments

Assessment is based on ambient monitoring by Des Moines Water Works and IDNR city monitoring.

Basis for Assessment

Had 14 of 18 non runoff-affected samples in violation of Class A WQ criterion (=78% viol =NS).   Only violations of Class B WQ criteria was mercury:  6 of 9 samples collected over 3 years exceeded the Class B WQ criterion (= 67% viol).   Due to problems with mercury analysis, and due to recommend in 305(b) guidelines (1996: 5-18) regarding reliability of toxics data < 1 ppb., these violations are not considered in the assessment.   Thus, Class B uses assessed as FST due to presumed impacts from NPS.   For Class C use, 14 of 68 samples had NO3 > 10 mg/l (= 20% viol).  Although both mean (7.45 mg/l) and median (7.5 mg/l) levels of NO3 were < 10 mg/l, assess as PS due to installation of nitrate removal system by DM W.Works.