Assessment Comments
Assessment is based on results of (1) ambient water quality monitoring at Des Moines and Runnells conducted from 2002-04 by ISU for the ACOE WQ study and (2) IDNR/UHL ambient monthly city monitoring dstr from Des Moines from 2002-04.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "not supporting" due to levels of indicator bacteria (E. coli) that exceed state water quality standards. The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported " based on results of ambient chemical/physical water quality monitoring show no violations of Class B(WW) criteria. 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) upstream from Red Rock Reservoir (ISU/ACOE Station 7 at County Road S35 near Runnells (STORET Station 17770003) as part of the Des Moines River Water Quality Study from 2002 through 2004 (see Lutz and Cummings 2003, Lutz 2004, and Lutz et al. 2005) and (2) IDNR/UHL ambient city monitoring downstream from Des Moines near Runnells in 2002 through 2004. This is the same assessment as that developed for the adjacent upstream assessment segment (IA 04-LDM-0040-2).
EXPLANATION: The Class A uses are assessed as "not supported" based on results of monitoring for indicator bacteria (E. coli). Due to recent changes in Iowa’s Water Quality Standards, Iowa’s 2006 assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses: the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff." Due to a change in the Standards in July 2003, E. coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E. coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.” Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E. coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of the 2006 Section 305(b) assessments and Section 303(d) listings.
Monitoring results from both ISU/ACOE and IDNR stations at Des Moines and near Runnells showed that the overall geometric means for E. coli (indicator) bacteria in summer periods of 2002, 2003, and 2004 (235 orgs/100 ml from IDNR/UHL; 405 orgs/100 ml from ISU/ACOE) were greater than the state WQ criterion of 126 organisms/100 ml. In addition, relatively high percentages of samples exceeded Iowa’s single sample maximum criterion for E. coli (235 orgs/100 ml): 11 of 24 samples (46%) at the IDNR/UHL station, and 14 of 25 samples (56%) at the ISU/ACOE station, exceeded this value. According to U.S. EPA guidelines for Section 305(b) reporting, and according to IDNR’s assessment/listing methodology, if the geometric mean of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Also, these EPA guidelines state that if more than 10% of the samples exceed the state’s single-sample maximum criterion, the primary contact recreation uses should be assessed as “partially supported”. According to IDNR’s assessment/listing methodology, the results from both monitoring agencies suggest that significantly greater than 10% of the samples exceed IDNR’s single-sample maximum value, thus suggesting that the Class A uses should be assessed as “partially supported/impaired”. Thus, the percentages of violations of Iowa’s single-sample maximum criterion (46% from IDNR/UHL monitoring and 56% from ISU/ACOE monitoring) also suggest impairment of the Class A uses.
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." No violations of Class B(WW) water quality criteria for conventional parameters (dissolved oxygen, pH, or ammonia-nitrogen) occurred in the combined 66 samples collected at the ISU/ACOE station during the 2002-2004 assessment period.
At the IDNR/UHL station, no violations of Class B(WW) water quality criteria for dissolved oxygen or pH occurred in the 36 samples collected during the 2002-2004 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.
Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this river segment.
