Assessment Comments
Assessment is based on (1) results of water quality monitoring conducted during the 2008-2010 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" 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 are assessed (monitored) as "fully supported" 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 2008-2010 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 Steffen 2009, Lutz 2010, and Lutz 2011) and on results of U.S. EPA/IDNR fish contaminant monitoring near Boone in 2009. In addition to routine ambient monitoring at ISU/ACOE Station 1 at County Road E26 northwest of Boone, sampling was also conducted at ISU/ACOE Station 0 at Highway 197 near Stratford due to flood conditions at ISU/ACOE Station 1. 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 25 samples collected during the recreational seasons of 2008 through 2010 at ISU/ACOE Station 1 north west of Boone were as follows: the 2008 geometric mean was 128 orgs/100 ml, the 2009 geometric mean was 56 orgs/100 ml, and the 2010 geometric mean was 402 orgs/100 ml. Two of the three geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Seven of the 25 samples (28%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.
The geometric means of indicator bacteria (E. coli) in the nine samples collected during the recreational seasons of 2008 and 2010 at ISU/ACOE Station 0 near Stratford were as follows: the 2008 geometric mean was 1,017 orgs/100 ml and 2010 geometric mean was 652 orgs/100 ml. Both geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Six of the nine samples (67%) 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 2008-2010 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, or dissolved oxygen occurred in the combined 75 samples collected at the ISU/ACOE monitoring stations NW of Boone and near Stratford during the 2008-2010 assessment period.
One of the 12 samples analyzed during this period for toxic metals contained a level of lead and copper above their respective Class B(WW1) criteria. According to IDNR’s assessment/listing methodology, and according to U.S. EPA assessment guidance, more than one violation of a toxic contaminant in a three-year period suggests impairment of the aquatic life use. Thus, the single violations of the Class B(WW1) criteria for lead and copper during the 2008-10 assessment period does not indicated impairment the aquatic life uses. No violations of Class B(WW1) criteria occurred in the 12 samples analyzed for other toxic metals (e.g., cadmium, mercury, nickel, and zinc).
Fish consumption uses were 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. Levels 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.
