Des Moines River IA 04-UDM-1214

Assessment Comments

Assessment is based on results of monitoring NW of Boone conducted by Iowa State Univ. in 2000-01 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 B(WW) aquatic life uses as fully supported/threatened.   Fish consumption uses were "not assessed."  EXPLANATION:  The assessments of support of the beneficial uses are based on results of water quality monitoring conducted at the CoR.  E-26 bridge northwest of Boone, IA, 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).   The only violation of Class B(WW) WQ criteria for conventional parameters at the ISU/ACOE monitoring station was in one of the 47 samples analyzed for dissolved oxygen during the biennial period.   The sample collected on July 6, 1999, contained 3.87 mg/l of dissolved oxygen; this level violated the criterion of 5.0 mg/l.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), the percentage of violations of the dissolved oxygen criterion at this station (2%) does not suggest a water quality impairment.   Levels of pH and ammonia-nitrogen did not violate the respective Class B(WW) criteria during the biennial period (n=47).   Due to the violation of the WQ criterion for dissolved oxygen this river reach in July 1999, the support of the Class B(WW) aquatic life uses was assessed as "fully supported / threatened."  This assessment ("threatened") presumes a minor impact to water quality and does not indicate a declining water quality trend.   In the nine samples analyzed for toxic metals (cadmium, copper, lead, mercury and zinc), 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 upstream (Dolliver State Park) and downstream (Saylorville Reservoir) 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.   Due to continuing uncertainty regarding the significance of mercury levels in the Des Moines River, the support of the Class B(WW) aquatic life uses was assessed as "fully supported / threatened."  This assessment ("threatened") presumes a minor impact to water quality and does not indicate a declining water quality trend.   For more information on ISU/ACOE water quality monitoring in this river reach, see Lutz et al.  (1999) and Lutz (2000).   Fish consumption uses were not assessed due to lack of recent monitoring information.   However, EPA/DNR (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.