Assessment Comments

Assessment is based on results of water quality monitoring conducted during the 2004-2006 assessment period 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. 2005, Lutz and Francois 2006, and Lutz and Francois 2007).

Basis for Assessment

[Note:  Prior to the current (2008) Section 305(b) cycle, this stream segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), and due to the completion of a Use Attainability Analysis in 2007, this segment is also now designated for Class A1 (primary contact recreation) uses.   This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on results of ambient monitoring for indicator bacteria (E.  coli).   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 remain “not assessed” due to the lack of recent fish contaminant monitoring in this river segment.   The assessments of support of the beneficial uses are based on results of water quality monitoring conducted during the 2004-2006 assessment period 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.  2005, Lutz and Francois 2006, and Lutz and Francois 2007).  

EXPLANATION:  The Class A1 uses are assessed (monitored) as "partially 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.  

The geometric mean level of indicator bacteria (E.  coli) in the 36 samples collected (127 orgs/100ml) during the recreational seasons of 2004 through 2006 is essentially equal to the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Given the variability in ambient levels of indicator bacteria, the geometric mean cannot be considered significantly greater than the Iowa water quality criterion of 126 orgs/100 ml.   Twelve of the 36 samples (33%), however, exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, if levels of E.  coli exceed the single-sample maximum criterion in more than 10% of the samples, the primary contact recreation uses should be assessed as “partially supported” (see pgs 3-33 to 3-35of U.S.  EPA 1997b).   According to IDNR’s assessment/listing methodology, these results suggest that the violation frequency of Iowa’s single-sample maximum criterion in this assessment segment is significantly greater than 10%, and thus these results suggest impairment of the Class A1 uses of this river segment.  

Results of bacterial monitoring from 2004-2006 at monitoring stations upriver from Saylorville Reservoir, suggest low levels of E.  coli in the upper Des Moines River.   For example, the three-year geometric means (N=24-36 samples) for stations near Boone (127 orgs/100 ml), downstream from Fort Dodge (99 orgs/100 ml), upstream from Fort Dodge (82 orgs/100 ml), and on the West Fork Des Moines River near Humboldt (103 orgs/100 ml) all met the Iowa Class A1 criterion of 126 E.  coli orgs/100 ml.   Although the percentage of samples greater than Iowa’s single-sample maximum criterion suggests impairment (“partial support”) at several of these stations, the difference between impairment and “full support” is typically one sample violation.   These results suggest generally low levels of indicator bacteria in the Des Moines River upriver from Saylorville Reservoir.  

Results of ambient water quality monitoring during the 2004-2006 assessment period suggest that the Class B(WW1) aquatic life uses should be assessed as “fully supported.”  The only violation of Class B(WW1) WQ criteria for conventional parameters at the ISU/ACOE monitoring station NW of Boone was in one of the 66 samples analyzed for dissolved oxygen during the 2004-2006 assessment period.   The sample collected on September 6, 2005 contained 4.1 mg/l of dissolved oxygen; thus violating Iowa’s Class B(WW1) criterion of 5.0 mg/l.   Levels of pH and ammonia-nitrogen did not violate the respective Class B(WW1) criteria during the assessment period (N = 66).   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 dissolved oxygen 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).   None of the 12 samples analyzed for toxic metals (cadmium, lead, and mercury) violated their respective Iowa water quality criteria.   Thus, these results suggest “full support” of the Class B(WW1) aquatic life uses in this segment of the Des Moines River.

Fish consumption uses remain not assessed due to lack of recent monitoring information.   However, U.S EPA/IDNR (RAFT) fish tissue monitoring in 1999 on the Des Moines River upstream from this reach at Dolliver State Park showed very low levels of all contaminants in composite samples of fillets from common carp and freshwater drum.   The following is excerpted from the 2006 assessment developed for waterbody IA 04-UDM-0040-2 (Des Moines River from near Kalo upriver to the Ft.  Dodge impoundment):  “Fish consumption uses were assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Dolliver State Park in 1999.   Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).   The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes.   Prior to 2006, IDNR used action levels published by the U.S Food and Drug Administration to determine whether consumption advisories should be issued for fish caught as part of recreational fishing in Iowa.   In an effort to make Iowa’s consumption more compatible with the various protocols used by adjacent states, the Iowa Department of Public Health, in cooperation with Iowa DNR, developed a risk-based advisory protocol.   This protocol went into effect in January 2006 (see http://www.iowadnr.gov/fish/news/consump.html for more information on Iowa’s revised fish consumption advisory protocol).   Because the revised (2006) protocol is more restrictive than the previous protocol based on FDA action levels; fish contaminant data that previously suggested “full support” may now suggest either a threat to, or impairment of, fish consumption uses.   This scenario, however, does not apply to the fish contaminant data generated from the 1999 RAFT sampling conducted in this assessment segment:  levels of all contaminants from this monitoring were below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses.”