Assessment Comments
Assessment is based on (1) results of monitoring at Des Moines & Runnells conducted by ISU for the ACOE WQ study and (2) IDNR ambient monthly city monitoring dstr from Des Moines.
Basis for Assessment
[Note: For the 2002 report, the previous waterbody segment for the Des Moines River (IA 04-LDM-0040-0), which extended 42 miles from the upper end of Red Rock Reservoir to the confluence with the Raccoon River at Des Moines, was split into three subsegments: (1) upper end of Red Rock Reservoir to South River (IA 04-LDM-0040-1), (2) South River to North River (IA 04-LDM-0040-2), and (3) North River to Raccoon River (IA 04-LDM-0010-3). See above for previous Section 305(b) assessments for the original 42-mile river reach.]
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "partially supporting." The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported." Fish consumption uses are "not assessed." 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) as part of the Des Moines River Water Quality Study (see Lutz et al. 2001 and Lutz and Esser 2002) and (2) IDNR ambient city monitoring downstream from Des Moines near Runnells. EXPLANATION: The Class A uses are assessed as "partially supported." Although monitoring results from ISU/ACOE and IDNR stations at Des Moines and near Runnells showed that geometric means for fecal coliform (indicator) bacteria in summer periods of 2000 and 2001 were less than the state WQ criterion of 200 organisms/100 ml, the relatively high percentages of samples exceeding the U.S. EPA-recommended single sample maximum value for fecal coliforms (400 orgs/100 ml) suggest only "partial support" of the primary contact recreation uses. At the ISU/ACOE monitoring station at Runnells, the geometric mean of the 12 non-runoff-affected samples collected during 2000 and 2001 was 141 orgs/100 ml, with six of the 18 samples (33%) of the samples exceeding the 400 organism/100 ml single sample maximum. Results at the IDNR monitoring station near Runnells were somewhat improved but similar, with a geometric mean of 121 orgs/100 ml (n=9) and with 14% of the samples exceeding the 400 organism/100 ml single sample maximum. According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of the samples collected 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). While these results suggest continued impairment of the primary contact recreation uses (see assessments for the 1998 and 2000 reports above), the occurrence of geometric mean levels below the state water quality criterion of 200 orgs/100 ml suggest potential improvement in levels of indicator bacteria in this river segment. Results from the both the ISU/ACOE and IDNR monitoring stations at Runnells suggest that the Class B(WW) aquatic life uses are "fully supported." No violations of Class B(WW) water quality criteria for conventional parameters (dissolved oxygen or ammonia-nitrogen) occurred in the combined 46 samples collected at the ISU/ACOE station or in the 14 samples collected at the IDNR station during the 2000=2001 biennial period. One of 46 samples from the ISU/ACOE station, 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). 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). Copper was detected in four consecutive monthly samples from March 22, 2001 through June 13, 2001, with levels ranging from 10 to 20 ppb; lead was detected in two consecutive samples (March 22 (10 ppb) and April 12, 2001 (30 ppb)); four samples from spring 2001 contained detectable levels of zinc, with a maximum value of 80 ppb. None of these metals values exceeded the Class B(WW) chronic criteria. Fish consumption uses were not assessed due to the lack of fish contaminant monitoring in this river segment.
