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." The assessments of support of the beneficial uses are based on results of water quality monitoring and fish kill reporting conducted during the 2000-2001 biennial period 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. 2001 and Lutz and Esser 2002). EXPLANATION: Class A uses were assessed (monitored) as "fully supported." 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 2000 and 2001 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 summers of 2000 and 2001 was 10 orgs/100 ml, with no samples exceeding the 400 organism/100 ml single sample maximum. The maximum value of all 16 samples collected at this station during summers of 2000 and 2001 was 170 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." The Class B(WW) aquatic life uses remained assessed as "not supported" due to repeated fish kills. No violations of Class B(WW) water quality criteria for conventional parameters (dissolved oxygen, pH, ammonia-nitrogen) occurred in the 46 samples collected at this station during the 2000-2001 biennial period. In the nine samples analyzed for toxic metals, the only violations were for mercury: seven of the nine samples analyzed for toxic metals during the 2000-01 biennial period contained levels of dissolved mercury above the Iowa WQ criterion for human health (fish) of 0.15 ug/l (none of the nine samples exceeded the Class B(WW) chronic aquatic life criterion of 2.1 ug/l (maximum value of the nine samples was 0.90 ug/l)). According to U.S. EPA guidelines for Section 305(b) reporting (U.S. EPA 1997b, page 3-18), more than one violation of a water quality criterion for a toxic contaminant within a three-year period indicates that the aquatic life uses are not fully supported. 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), (2) the historical lack of high levels of mercury in fish tissue samples from this reach of river, and (3) a recent study of mercury levels in the Des Moines River near Des Moines (see assessment for the 2000 report above), data for mercury in water were not used to assess support of the Class B(WW) aquatic life uses of this river reach. Regardless, the continuing uncertainty regarding the significance of mercury levels in the Des Moines River suggests that the assessment of support of the Class B(WW) aquatic life should remain "fully supported / threatened." Two fish kills were reported for this river reach during the 2000-2001 biennial period. These kills occurred on May 24, 2000 and August 14, 2001 immediately downriver from Red Rock Dam. Both kills were relatively minor and involved channel catfish, freshwater drum and/or white bass. Fish killed in both events exhibited signs of gas bubble trauma (see Lutz et al. 2001:175 and Lutz and Esser 2002:207). According to DNR's assessment methodology for Section 305(b) reporting, occurrence of more than one fish kill 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. Fish contaminant monitoring conducted downstream from Red Rock Reservoir by ISU/ACOE in 2000 and 2001 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. (2001) and Lutz and Esser (2002).
