Assessment Comments

Assessment is based on results of monitoring NW of Boone conducted by Iowa State Univ. from 2000-02 as part of the ACOE's Des Moines R./Saylorville Res./Red Rock Res. water quality study.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses remain assessed (monitored) as "fully supported / threatened" based on results of ambient chemical/physical water quality monitoring that show potential problems with levels of mercury in water.   Fish consumption uses remain “not assessed” due to the lack of recent fish contaminant monitoring in this river segment.   The assessments of support of the beneficial uses are based on results of water quality monitoring conducted during the 2000-2002 assessment period by Iowa State University (under contract with the U.S.  Army Corps of Engineers) (ISU/ACOE) as part of the Des Moines River Water Quality Study (see Lutz et al.  2001, Lutz and Esser 2002, and Lutz and Cummings 2003).  

EXPLANATION:  The only violation of Class B(WW) WQ criteria for conventional parameters at the ISU/ACOE monitoring station NW of Boone was in two of the 66 samples analyzed for dissolved oxygen during the 2000-2002 assessment period.   The sample collected on May 9, 2000, contained 3.2 mg/l of dissolved oxygen; the sample collected on August 6, 2002 contained 4.6 mg/l of dissolved oxygen; these levels violated the Class B(WW) criterion of 5.0 mg/l.   Levels of pH and ammonia-nitrogen did not violate the respective Class B(WW) criteria during the assessment period (N approximately = 66).   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), the percentage of violations for dissolved oxygen at this station (3%) does not suggest a water quality impairment (the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated).   In the samples analyzed for toxic metals (cadmium, lead, and mercury), the only violations were for mercury:  in the 10 samples analyzed for toxic metals, the only violations were for mercury:  four of the 10 samples analyzed 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 ten 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."  This assessment ("threatened") presumes a minor impact to water quality and does not indicate a declining water quality trend.  

Fish consumption uses were not assessed due to lack of recent monitoring information.   However, U.S EPA/IDNR (RAFT) fish tissue monitoring in 1999 on the Des Moines River upstream from this reach at Dolliver State Park showed very low levels of all contaminants in composite samples of fillets from common carp and freshwater drum.   Levels of most contaminants were below the laboratory detection level, and levels of the detected contaminants were less than ½ of respective FDA action levels and DNR levels of concern.