Des Moines River IA 04-LDM-1020

Assessment Comments

Assessment is based on IDNR ambient monthly city monitoring dstr from Des Moines.

Basis for Assessment

Had no violations of toxic criteria in the 46 samples collected at each of the monitoring stations over the 1996-97 period.   One of 12 samples analyzed for toxic metals exceeded the chronic WQ criterion for copper (8% violation).  1998 Section 305(b) assessment guidelines allow one violation for toxics in an abundant data set with the water fully supporting designated uses.   Eight of 11 samples (73% violation) exceeded the chronic WQ criterion for mercury; due to problems with analysis and with trace levels of toxic metals, did not use these data to develop the assessment.   Thus, consider the Class B(WW) aquatic life use as FST.   Levels fecal coliform bacteria at both stations indicate NS of the Class A primary contact uses:  in the 16 non-flow affected samples collected during summers of 1996 and 97, geometric means at both stations exceeded 200 orgs/100 ml, and 38% of the samples at both stations exceeded 400 orgs/100 ml (see page 3-34 of the 1998 305(b) Guidelines Supplement).   Continue to assess support of the fish consumption uses as FST.   Results of the 1997 RAFT fish contaminant monitoring program show that the level of tech.  chlordane (0.21 ppm) in the composite whole-fish sample of carp was greater than 1/2 of the FDA action level for chlordane (=0.300 ppm).   Follow-up monitoring will be conducted as part of future RAFT trend monitoring.   Level of mercury (0.198 ppm) was well below 1/2 of the FDA action level of 1.0 ppm.