Assessment Comments

Assessment is based on (1) results of monitoring by Iowa State Univ. for the ACOE's WQ project, (2) ambient monitoring by Des Moines Water Works, (3) IDNR city monitoring, and (4) fish tissue (RAFT) monitoring.

Basis for Assessment

Had 6 of 14 non-runoff affected samples in viol of Class A WQ criterion.  According to Section 305(b) guidelines (p.  3-34), the geometric mean of 241 organisms/100 ml and 29% of samples >400 organisms/100 ml suggests nonsupport of Class A uses.  Sources of fecals include agriculture & wildlife.  No viols of Class B(WW) WQ criteria for conventional pollutants in 46 samples collected during the 1996-97 period.   Nine of 11 samples exceeded the chronic WQ criterion for mercury; however, due to problems with mercury analysis, disregarded data for assessment purposes.  For Class C use, 24 of 67 samples collected from 1995-97 exceeded the nitrate MCL (=36%); mean/median NO3=7.66/7.77 mg/l.   Based on Section 305(b) guidelines for assessing support of drinking water uses (page 3-44), the use of the nitrate removal system by the DMWW constitutes "more than conventional treatment" and indicates that the designated drinking water use is partially supported (PS).   Results of 1993 RAFT show no fish contaminants > 1/2 FDA action levels; fish cons.  uses = FS.