Assessment Comments
Assessment is based on: (1) water quality monitoring conducted from 2010-2012 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, (2) IDNR/UHL ambient city monitoring downstream from Des Moines near Runnells from 2010 through 2012, and (3) results of 2006 fish contaminant monitoring conducted as part of the IDNR/UHL REMAP biological monitoring project (REMAP Site 221).
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supporting" (IR 4a) 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" (IR 2a) based on results of ambient chemical/physical water quality monitoring. Fish consumption uses remain assessed (monitored) as "fully supported" based on results of IDNR/UHL fish contaminant monitoring in 2006. The assessments of support of the beneficial uses are based on results of (1) water quality monitoring conducted from 2010-2012 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 2011, 2012 & 2013), (2) IDNR/UHL ambient city monitoring downstream from Des Moines near Runnells from 2010 through 2012 (STORET station 10770003), and (3) results of 2006 fish contaminant monitoring conducted as part of the IDNR/UHL REMAP biological monitoring project (REMAP Site 221).
Note: A TMDL for bacteria was prepared by IDNR and approved by U.S. EPA in March 2010. Because this TMDL covers all the identified impairments for the assessment segment, this segment is moved to IR Category 4a (TMDL approved).
EXPLANATION: The Class A1 primary contact recreation uses are assessed (monitored) as "not supported" based on results of monitoring for indicator bacteria (E. coli) at both the IDNR ambient station and the ISU/ACOE station near Runnells. The geometric means of indicator bacteria (E. coli) in the 24 samples collected during the recreational seasons of 2010 through 2012 at IDNR station 10770003 downstream from Des Moines were as follows: the 2010 geometric mean was 112 orgs/100 ml, the 2011 geometric mean was 45 orgs/100 ml and the 2012 geometric mean was 139 orgs/100 ml. Only the 2012 geometric mean very slightly exceed the Class A1 criterion of 126 orgs/100 ml; the 2010 and 2011 geometric means were below (met) the Class A1 criterion. Six of the 24 samples (25%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.
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 7 were as follows: the 2010 geometric mean was 177 orgs/100 ml, the 2011 geometric mean was 31 orgs/100 ml and the 2012 geometric mean was 71 orgs/100 ml. Only the 2010 geometric mean slightly exceed the Class A1 criterion of 126 orgs/100 ml. Five of the 29 samples (17%) 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.” Regardless of the impairment, levels of indicator bacteria in this river segment were relatively low during the 2010-2012 assessment period.
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 dissolved oxygen, pH, temperature, or ammonia-nitrogen, chloride or sulfate occurred in the 36 samples collected at the IDNR/UHL station during the 2010-2012 assessment period. At the ISU/ACOE station, no violations of Class B(WW1) water quality criteria for dissolved oxygen, ammonia, temperature, or pH occurred in the 66 samples collected during the 2010-2012 assessment period.
Fish consumption uses remain assessed (evaluated) as “fully supported” based on results fish contaminant monitoring conducted in this assessment segment in September 2006 as part of the IDNR/UHL REMAP project (Site 221). This monitoring showed low levels of the primary contaminants in the composite samples of common carp fillets: mercury: 0.239 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 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 2006 REMAP sampling conducted in this assessment segment shows that the levels of contaminants do not exceed any of the IDPH/IDNR consumption advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
