Assessment Comments

Assessment is based on results of water quality monitoring conducted during the 2006-2008 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.

Basis for Assessment

[Note:  Prior to the 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 "not 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 2006-2008 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 and Francois 2007, Lutz and Francois 2008, and Lutz and Steffen 2009).   Note:  this is the same assessment as that developed for the adjacent upriver segment, IA 04-UDM-0030_2.

EXPLANATION:  The Class A1 uses are assessed (monitored) as "not supported" based on results of monitoring for indicator bacteria (E.   coli).   The geometric mean level of indicator bacteria (E.   coli) in the 34 samples collected (139 orgs/100ml) during the recreational seasons of 2006 through 2008 is slightly above the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Ten of the 34 samples (29%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.  According to U.S.  EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level 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).  

Results of ambient water quality monitoring during the 2006-2008 assessment period suggest that the Class B(WW1) aquatic life uses should be assessed (monitored) as “fully supported.”  No violation of Class B(WW1) WQ criteria for ammonia, pH, or dissolved oxygen occurred in the 66 samples collected at the ISU/ACOE monitoring station NW of Boone during the 2006-2008 assessment period.   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.   The fish contaminant data generated from the 1999 RAFT sampling conducted in this assessment segment suggest that the levels of all contaminants from this monitoring were below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses.”