Assessment Comments

Assessment is based on (1) results of water quality monitoring conducted during the 2010-2012 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 and (2) results of U.S. EPA/IDNR fish contaminant monitoring near Boone in 2009.

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, 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" (IR 5a) based on results of ambient monitoring for indicator bacteria (E.  coli).   The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" (IR 2a) based on results of ambient chemical/physical water quality monitoring.   Fish consumption uses remain assessed (monitored) as "fully supported" (IR 2a) based on results of U.S.  EPA/IDNR fish tissue monitoring in 2009.   The assessments of support of the beneficial uses are based on results of water quality monitoring conducted during the 2010-2012 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 2011, 2012 and 2013) and on results of U.S.  EPA/IDNR fish contaminant monitoring near Boone in 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 means of indicator bacteria (E.  coli) in the 29 samples collected during the recreational seasons of 2010 through 2012 at ISU/ACOE Station 1 north west of Boone were as follows:  the 2010 geometric mean was 402 orgs/100 ml, the 2011 geometric mean was 98 orgs/100 ml, and the 2012 geometric mean was 60 orgs/100 ml.   Only one of the three geometric means (2008) exceed the Class A1 criterion of 126 orgs/100 ml.   Ten of the 29 samples (34%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”  

Results of ambient water quality monitoring during the 2010-2012 assessment period suggest that the Class B(WW1) aquatic life uses should be assessed (monitored) as “fully supported.”  No violations of Class B(WW1) WQ criteria for ammonia, pH, temperature, or dissolved oxygen occurred in the 66 samples collected at the ISU/ACOE monitoring station NW of Boone during the 2010-2012 assessment period.   None of the 12 samples analyzed for chloride and sulfate exceeded their respective criteria.   None of the 10 samples analyzed during this period for toxic metals (e.g., cadmium, cipper, mercury, and lead) violated the respective Class B(WW1) criteria.   According to IDNR’s assessment/listing methodology, and according to U.S.  EPA assessment guidance, these results suggest “full support” of the aquatic life uses.

Fish consumption uses remain assessed (monitored) as “fully supported” based on results of U.S.   EPA/IDNR fish contaminant (RAFT) monitoring at the Des Moines River near Boone in 2009.   The composite samples of fillets from common carp and walleye had low levels of contaminants.   Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.2 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm.   The level of mercury in the composite sample of walleye fillets was 0.181 ppm.   The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses.    The fish contaminant data generated from the 2009 RAFT sampling conducted at this river show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.   In addition, results of water quality monitoring show that none of the toxic metals analyzed (e.g., cadmium, copper, and mercury) exceeded their respective Human Health (fish) water quality criteria.