Assessment Comments
Assessment is based on results of the following monitoring programs from 2000-02: (1) water quality monitoring at Sycamore Access conducted by ISU as part of ACOE's WQ study (including fish contaminant monitoring, (2) ambient monitoring by Des Moines Water Works, (3) IDNR/UHL ambient city monitoring at Sycamore Access.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supported" based on results of ambient monitoring for indicator bacteria. The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported / threatened." The Class C drinking water uses are assessed (monitored) as "partially supported" due to high levels of nitrate. Fish consumption uses are assessed as "fully supported" based on results of annual fish contaminant monitoring. The assessments of support of the beneficial uses are based on results of (1) water quality monitoring conducted during the 2000-2002 assessment period approximately two miles downstream from Saylorville Dam at Sycamore Access (NW 66th Street) 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, Lutz and Cummings 2003), (2) monitoring conducted on the Des Moines River by the Des Moines Water Works during the 2000-2002 assessment period, and (3) results of IDNR/UHL ambient city monitoring upstream from Des Moines at the Sycamore Access (NW 66th Street; station 10770002) during the 2000-2002 assessment period.
EXPLANATION: Results from the ISU/ACOE monitoring station located approximately two miles downstream from Saylorville Dam continue to suggest that Class A uses are fully supported. The geometric mean of fecal coliform bacteria in the 26 non-runoff affected samples collected during summers of 2000, 2001, and 2001 (10 orgs/100 ml) is well below the state WQ criterion of 200 orgs/100 ml; none of the 26 samples contained a level of fecal coliforms above the EPA-recommended single sample maximum value of 400 orgs/100 ml (maximum value was 170 orgs/100 ml. These results indicate extremely low levels of bacteria in this river segment.
The Class B(WW) aquatic life uses remain assessed as "fully supported / threatened" due to results of ambient monitoring that indicate the potential for elevated levels of mercury in this river segment. Results from ISU/ACOE monitoring at the Sycamore Access station show no violations of Class B(WW) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the approximately 66 samples collected at this station during the 2000-2002 assessment period. In the samples analyzed for toxic metals, the only violations were for mercury: two of the 10 samples analyzed for dissolved mercury during the 2000-2002 assessment period contained levels of above the Iowa Class B(WW) human health criterion of 0.15 ppb. None of the 10 samples contained levels of mercury above the Class B(WW) chronic criterion for mercury of 2.1 ppm. 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."
Results from the IDNR city monitoring station at Sycamore Access suggest that the Class B(WW) aquatic life uses are "fully supported." None of the 28 samples collected during the 2000-2002 assessment period exceeded Class B(WW) criteria for dissolved oxygen, pH, or ammonia-nitrogen. None of the 28 samples analyzed for toxic metals (including mercury), and none of the nine samples analyzed for pesticides and other toxic organic compounds, exceeded Class B(WW) criteria.
The Class C (drinking water) uses are assessed (monitored) as "partially supporting" due to high levels of nitrate in the Des Moines River. Results of monitoring by the Des Moines Water Works in this river segment that show that over 27% of the samples collected during the 2000-2002 assessment period (104 of 405) contained nitrate above the 10 mg/l MCL (mean = 7.6 mg/l; median = 8.0 mg/l; maximum = 13.2 mg/l). According to IDNR’a assessment methodology, if more than 25% of the samples exceed the state water quality standard for nitrate (=the MCL of 10 mg/l), the Class C (drinking water) uses should be assessed as “not supported.” Due, however, to over-sampling by water supply utilities during times of year when nitrate levels tend to be high, the use of a simple percentage of samples in violation of the MCL likely overestimates the percentage of time that nitrate levels actually exceed the MCL. Thus, to correct for this bias, IDNR staff summarized the Des Moines River nitrate data from the Des Moines Water Works as weekly averages and compared these averages to the water quality standard. Nineteen of the 145 weekly average nitrate levels (13%) for the period 2000-2002 exceeded the standard (weekly mean=5.9 mg/l; weekly median=6.0 mg/l; maximum weekly average=12.8 mg/l). According to IDNR's assessment guidelines, if between 10% and 25% of the samples exceed the MCL for nitrate, the Class C uses are assessed as “partially supported.” Thus, according to IDNR's assessment guidelines, the DMWW data--whether summarized as individual samples or as weekly averages--suggest that the Class C drinking water uses are "partially supported." In addition, the continued periodic use of a nitrate removal system by the Des Moines Water Works also suggests an impairment to drinking water uses due to high levels of nitrate in the Des Moines River. According to U.S. EPA's 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 thus indicates that the designated drinking water uses are not fully supported (=impaired).
Results of monitoring conducted at Sycamore Access as part of the ISU/ACOE network show a similar impact of nitrate on drinking water uses: 12% of the samples collected during the 2000-2002 assessment period (8 of 66 samples) exceeded the nitrate MCL (mean = 6.0 mg/l; maximum = 12.7 mg/l). Although fewer samples were collected, results of IDNR city monitoring at Sycamore Access suggest a lesser impact on drinking water uses from nitrate with only 7% of samples (2 of 28 samples) exceeding the nitrate MCL (mean 6.2 mg/l; maximum = 13.0 mg/l). The results of IDNR/UHL monitoring for nitrate would suggest that drinking water uses should be assessed as "fully supported / threatened" (according to IDNR assessment guidelines for Section 305(b) reporting, if the nitrate MCL is exceeded, but less than 10 percent of the samples collected during the biennial period exceed the MCL, the drinking water uses are assessed as "fully supported / threatened"). Nonetheless, the more robust data set for nitrate from the Des Moines Water Works is used to justify assessing the drinking water uses of this river segment as "impaired."
Results of monitoring during the 2000-2002 assessment period as part of IDNR ambient city monitoring and by the Des Moines Water Works show relatively low levels of atrazine in this segment of the Des Moines River. None of 28 samples analyzed for the IDNR network contained a level of atrazine above the MCL of 3.0 ug/l (mean atrazine = 0.23 ug/l; maximum = 1.1 ug/l. None of the 20 river samples analyzed by the Des Moines Water Works between April 2001 and April 2002 exceeded the MCL for atrazine of 3.0 ug/l (mean and median=1.2 ug/l; maximum=3.3 ug/l (rounding is required when comparing sample values to the MCL of 3 ug/l; thus levels of atrazine below 3.5 round down to 3 ug/l and do not exceed the MCL). According to IDNR guidelines for Section 305(b) assessments, these results do not suggest an impairment of drinking water uses due to atrazine.
Fish contaminant monitoring conducted downstream from Saylorville Reservoir by ISU/ACOE in 2000, 2001, and 2002 showed that levels of contaminants (dieldrin, chlordane, alachlor, trifuluralin, and chlorpyrifos) in composite samples of whole fish common carp (2000, 2001 & 2002) and common carp fillets (2001) were all less than ½ of the respective FDA action levels or DNR levels of concern (ISU/ACOE fish tissue samples are not analyzed for mercury). Thus, fish consumption uses remain assessed as "fully supported."
