Assessment Comments

Assessment is based on (1) results of monitoring by Iowa State Univ. for the ACOE's WQ project, (2) ambient monitoring by Des Moines Water Works, (3) IDNR city monitoring, and (4) fish tissue (RAFT) monitoring.

Basis for Assessment

SUMMARY:  Continue to assess support of the Class A (primary contact recreation) uses as "not supported" and the Class B(WW) aquatic life uses as fully supported/threatened.   The assessment for Class C (drinking water) uses remain assessed as "not supported."  Fish consumption uses remain assessed as fully supported.   EXPLANATION:  The assessments of support of the beneficial uses are based primarily 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 at Van Meter continue to suggest that Class A uses are not supported.   A total of 18 samples were analyzed for levels of indicator bacteria (fecal coliforms) during summers of 1998 and 1999.   The geometric mean of fecal coliform bacteria in the 10 non-runoff-affected samples collected during this period (453 orgs/100 ml) is well above the state WQ criterion of 200 orgs/100 ml, and well over 10% of these samples (50%) exceeded the EPA-recommended single sample maximum value of 400 orgs/100 ml.   Thus, according to U.S.  EPA guidelines for Section 305(b) reporting (see U.S.  EPA 1997b, pages 3-33 to 3-35), the monitoring results from the Van Meter station suggest nonsupport of the designated primary contact recreation uses.   Results from this monitoring station 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 (dissolved oxygen, pH, and ammonia-nitrogen) 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 and Raccoon rivers near Des Moines, the assessment of support of the Class B(WW) aquatic life uses was downgraded from "fully supported" to "fully supported / threatened."  The level of use support for the Class C (drinking water) uses remained assessed as "not supporting" due to (1) results from the ISU/ACOE monitoring station that show that 15 of the 47 samples (32%) collected during the 1998-99 biennial period contained nitrate above the 10 mg/l MCL, (2) DNR's assessment methodology that states that greater than 25% violation of the nitrate MCL suggests nonsupport of drinking water uses, and (3) use of a nitrate removal system by the Des Moines Water Works (based on  Section 305(b) guidelines (page 3-44 of U.S.  EPA 1997b), the use of the nitrate removal  system by the DMWW constitutes "more than conventional  treatment" and indicates that the designated drinking water use is partially supported (=impaired).   For more information on ISU/ACOE water quality monitoring in this river reach, see Lutz et al.  (1999) and Lutz (2000).   EPA/DNR fish tissue (RAFT) monitoring conducted near Booneville in 1999 showed that levels of contaminants in the composite sample of carp fillets were less than ½ of the respective FDA action levels and DNR levels of concern for organochlorine contaminants and mercury.   Thus, fish consumption uses were assessed as "fully supported."