Assessment Comments
Basis for Assessment
SUMMARY: Continue to assess support of the Class B(WW) aquatic life uses as fully supported/threatened. Fish consumption uses remain assessed as fully supported. EXPLANATION: The assessments of support of the beneficial uses are based on results of water quality monitoring conducted by Iowa State University (under contract with the U.S. Army Corps of Engineers) as part of the Des Moines River Water Quality Study (see Lutz et al. 1999 and Lutz 2000). Results from the ISU/ACOE monitoring station located approximately two miles downstream from Saylorville Dam (=Sycamore Access) suggest that the Class B(WW) aquatic life uses are fully supported/threatened (=FST). No violations of Class B(WW) water quality criteria for conventional parameters occurred in the 47 samples collected at this monitoring station during the 1998-99 biennial period. In the nine samples analyzed for toxic metals, the only violations were for mercury: all nine samples analyzed for toxic metals during the 1998-99 biennial period contained levels of dissolved mercury above the Iowa WQ criterion of 0.05 ug/l. Due, however, 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) the 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 assess support of the Class B(WW) aquatic life uses of this river reach. In addition, a recent study (Montgomery and Watson 1998) was conducted to determine whether levels of mercury in the vicinity of Des Moines presented a water quality problem. Study results showed that (1) average levels of mercury in the Des Moines River ranged from 2.7 to 2.8 ng/l and were well below the Iowa water quality criterion of 50 ng/l; (2) levels of mercury in effluent of the Des Moines wastewater treatment plant averaged 3.30 ng/l but account for only 1.7 percent of the total river mercury load leaving the city of Des Moines, (3) mercury levels in Des Moines River fish (maximum of 0.179 ppm) were well below the FDA action level of 1.0 ppm, (4) most of the mercury loading seen at Des Moines comes from upstream areas in the Des Moines and especially the Raccoon river basins, and (5) river mercury concentrations were strongly correlated to total suspended solids concentrations. Due to continuing uncertainty regarding the significance of mercury levels in the Des Moines River, the assessment of support of the Class B(WW) aquatic life uses was downgraded from "fully supported" to "fully supported / threatened." Fish contaminant monitoring conducted downstream from Saylorville Reservoir by ISU in 1998 and 1999 showed that levels of contaminants (dieldrin, chlordane, alachlor, trifluralin, and chlorpyrifos) in composite samples of whole fish common carp (98 & 99) and common carp fillets (98) were all less than ½ of the respective FDA action levels or DNR levels of concern. Thus, fish consumption uses were assessed as fully supported. For more information on ISU/ACOE water quality monitoring in this river reach, see Lutz et al. (1999) and Lutz (2000).
