Assessment Comments
Assessment is based on: results of (1) water quality monitoring conducted from 2004-2006 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 (see Lutz et al. 2005, Lutz and Francois 2006, and Lutz and Francois 2007) and (2) IDNR/UHL ambient city monitoring downstream from Des Moines near Runnells from 2004 through 2006 (STORET station 10770003).
Basis for Assessment
SUMMARY: The Class A1 (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(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient chemical/physical water quality monitoring. Fish consumption uses are "not assessed" due to the lack of fish contaminant monitoring in this assessment segment. The assessments of support of the beneficial uses are based on results of (1) water quality monitoring conducted from 2004-2006 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 (see Lutz et al. 2005, Lutz and Francois 2006, and Lutz and Francois 2007) and (2) IDNR/UHL ambient city monitoring downstream from Des Moines near Runnells from 2004 through 2006 (STORET station 10770003). This is the same assessment as that developed for the adjacent upstream assessment segment (IA 04-LDM-0040-2).
EXPLANATION: The Class A1 primary contact recreation uses are assessed (monitored) 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 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 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 2004, 2005, and 2006 (166 orgs/100 ml from IDNR/UHL; 198 orgs/100 ml from ISU/ACOE) were greater than the state WQ criterion of 126 organisms/100 ml. In addition, moderately high percentages of samples exceeded Iowa’s single sample maximum criterion for E. coli (235 orgs/100 ml): 7 of 24 samples (29%) at the IDNR/UHL station, and 16 of 35 samples (46%) 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 criterion, thus suggesting that the Class A1 uses should be assessed as “partially supported/impaired.” Thus, the percentages of violations of Iowa’s single-sample maximum criterion (29% from IDNR/UHL monitoring and 46% from ISU/ACOE monitoring) also suggest impairment of the Class A1 uses. Note: both the geometric means and the percentages of samples that exceeded Iowa’s single sample maximum criterion in this river segment declined from the 2002-2004 to the current (2004-2006) assessment periods. At the IDNR/UHL station, the geometric mean declined from 235 to 166 orgs/100ml and the percentage greater than the single-sample maximum criterion declined from 46 to 29%. At the ISU/ACOE station, the geometric mean declined from 405 to 198 orgs/100ml and the percentage greater than the single-sample maximum declined from 56 to 46%. While nonetheless still indicating impairment of the Class A1 uses, the levels of E. coli during the 2004-2006 assessment period do appear to have declined. Whether this decline (i.e., improvement) is related to human or natural (weather) causes is unknown.
Results from the both the ISU/ACOE and IDNR/UHL monitoring stations at Runnells suggest that the Class B(WW1) aquatic life uses should be assessed (monitored) as "fully supported." No violations of Class B(WW1) water quality criteria for conventional parameters (dissolved oxygen, pH, or ammonia-nitrogen) occurred in the 36 samples collected at the IDNR/UHL station during the 2004-2006 assessment period. Also, none of the 14 samples analyzed for toxic metals, and none of the nine samples analyzed for pesticides, exceeded the respective Class B(WW1) criteria.
At the ISU/ACOE station, no violations of Class B(WW1) water quality criteria for ammonia or pH occurred in the 66 samples collected during the 2004-2006 assessment period. One of these samples, however, exceeded the Class B(WW1) criterion for dissolved oxygen. The sample collected on August 14, 2006, contained a dissolved oxygen level of 4.96 mg/l, thus very slightly violating the Class B(WW1) criterion of 5.0 mg/l. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of less than 10 % for conventional parameters such as dissolved oxygen nonetheless suggests "full support" of aquatic life uses. Thus, the percentage of violation of the dissolved oxygen criterion at this station (2%) does not suggest an impairment of aquatic life uses in this stream segment.
Fish consumption uses are "not assessed" due to the lack of fish contaminant monitoring in this assessment segment.
