Assessment Comments
Assessment is based on results of monitoring conducted by Iowa State Univ. as part of the ACOE's Des Moines R./Saylorville Res./Red Rock Res. water quality study.
Basis for Assessment
SUMMARY: Continue to assess support of the Class A (primary contact recreation) uses as "fully supporting," the Class B(WW) aquatic life uses as "not supported," and the fish consumption uses as "fully supported". EXPLANATION: The assessments of support of the beneficial uses are based on results of water quality monitoring and fish kill reporting 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). Monitoring results from the ISU/ACOE station 0.7 mi downstream from Red Rock Dam showed that (1) geometric means for fecal coliform (indicator) bacteria in summer periods of 1998 and 1999 were well below the state WQ criterion of 200 organisms/100 ml and (2) no samples exceeded the U.S. EPA-recommended single sample maximum value for fecal coliforms (400 orgs/100 ml). At this monitoring station, the geometric mean of the 6 non-runoff-affected samples collected during 1998 and 1999 was 19 orgs/100 ml, with 0% of the samples exceeding the 400 organism/100 ml single sample maximum. The maximum value of all 18 samples collected at this station during summers of 1998 and 1999 was 63 orgs/100 ml, thus indicating extremely low levels of indicator bacteria in this reach of river. According to U.S. EPA guidelines for Section 305(b) reporting, if geometric means for fecal coliforms are less than 200 organisms/100 ml, and if less than 10% of samples exceed 400 orgs/100 ml, the primary contact recreation uses are "fully supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Results from this ISU/ACOE monitoring station suggest that the Class B(WW) aquatic life uses are "fully supported/threatened." No violations of Class B(WW) water quality criteria for conventional parameters (dissolved oxygen, pH, ammonia-nitrogen) occurred in the 47 samples collected at this 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 Red Rock Reservoir by ISU/ACOE in 1998 and 1999 showed that levels of contaminants (dieldrin, chlordane, alachlor, trifuluralin, and chlorpyrifos) in composite samples of whole fish and fillets of common carp 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). Four fish kills were reported for this river reach during the 1998-1999 biennial period. These kills occurred on September 20, 1998; August 20, 1999, August 31, 1999; and September 14, 1999. Relatively few fish were reported for these kills, with from six to 80 fish reported for the four kills. All kills were attributed to gas bubble trauma (see Lutz et al. 1999:171 and Lutz 2000:181-182). According to DNR's assessment methodology for Section 305(b) reporting, occurrence of more than two fish kills during the most recent three-year period suggests that the aquatic life uses are "not supported." Thus, the Class B(WW) aquatic life uses of this river reach remained assessed as "not supported" due to repeated fish kills.
