Assessment Comments
Assessment is based on results of (1) ambient water quality monitoring at Des Moines and Runnells conducted from 2000-02 by ISU for the ACOE WQ study and (2) IDNR/UHL ambient monthly city monitoring dstr from Des Moines from 2000-02.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "not supporting" due to levels of indicator bacteria that exceed state water quality standards. The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported / threatened" based on results of ambient chemical/physical water quality monitoring that showed a single violation of state criteria for ammonia-nitrogen. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment. The assessments of support of the beneficial uses are based on results of (1) water quality monitoring conducted 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 from 2000 through 2002 (see Lutz et al. 2001, Lutz and Esser 2002, and Lutz and Cummings 2003) and (2) IDNR/UHL ambient city monitoring downstream from Des Moines near Runnells from April 2000 through December 2002.
EXPLANATION: The Class A uses are assessed as "not supported" based on results of monitoring for indicator bacteria (fecal coliforms). For purposes of Section 305(b) assessments, DNR uses the long-term average monthly flow plus one standard deviation of this average to identify river flows that are materially affected by surface runoff. According to the Iowa Water Quality Standards (IAC 1990:8), the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) does not apply "when the waters are materially affected by surface runoff." Fourteen of the 16 samples collected from the IDNR/UHL station, and all 26 samples collected from the ISU/ACOE station during the 2000, 2001, and 2002 recreational seasons were collected at flows not materially affected by surface runoff. Monitoring results from both ISU/ACOE and IDNR stations at Des Moines and near Runnells showed that the overall geometric means for fecal coliform (indicator) bacteria in summer periods of 2000, 2001, and 2002 (215 orgs/100 ml from IDNR/UHL; 261 orgs/100 ml from ISU/ACOE) were greater than the state WQ criterion of 200 organisms/100 ml. In addition, relatively high percentages of samples exceeded the U.S. EPA-recommended single sample maximum value for fecal coliforms (400 orgs/100 ml): four samples (29%) at the IDNR/UHL station, and 13 samples (50%) at the ISU/ACOE station, exceeded this value. According to U.S. EPA guidelines for Section 305(b) reporting, if the geometric mean is greater than 200 orgs/100ml, the primary contact recreation uses are "not supported”; in addition, if more than 10% of the samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are "partially supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, both the geometric mean values of fecal coliforms and the percentages of samples that exceed the single-sample maximum value of 400 orgs/100 ml suggest impairment of the Class A (primary contact recreation) uses of this river segment.
Results from the both the ISU/ACOE and IDNR/UHL monitoring stations at Runnells suggest that the Class B(WW) aquatic life uses are "fully supported / threatened." No violations of Class B(WW) water quality criteria for conventional parameters (dissolved oxygen or ammonia-nitrogen) occurred in the combined 66 samples collected at the ISU/ACOE station during the 2000-2002 assessment period. One of the 66 samples, however, exceeded the Class B(WW) criterion for pH. The sample collected on September 4, 2001, contained a pH level of 9.02 units, thus slightly exceeding the water quality criterion of 9.0 pH units. 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 pH at this station (2%) 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).
At the IDNR/UHL station, no violations of Class B(WW) water quality criteria for dissolved oxygen or pH occurred in the 28 samples collected during the 2000-2002 assessment period. One of these samples, however, exceeded the Class B(WW) criterion for ammonia-nitrogen. The sample collected on April 3, 2002, contained a ammonia nitrogen at 1.2 mg/l, thus exceeding the criterion of 1.09 mg/l. According to U.S. EPA guidelines for Section 305(b) reporting (U.S. EPA 1997b, page 3-18), uses are “fully supported” if chronic criteria for a toxic pollutant (for example, ammonia) are exceeded in up to one sample from an dataset based on monthly monitoring. IDNR assessment guidelines, however, specify that one violation of a toxic parameter (e.g., ammonia) indicates a “threat” to full support of the designated uses. Although not indicating impairment of aquatic life uses, the frequency of detection of metals in samples collected at the IDNR station was relatively high for ambient monitoring stations on Iowa rivers (metals were not analyzed in samples from the ISU/ACOE station). In the 28 samples collected during the 2000-2002 assessment period, copper was detected in five samples, lead in three samples, and zinc in six samples. None of these metals values exceeded the Class B(WW) chronic criteria.
Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this river segment.
