Assessment Comments
Assessment is based on: results of (1) water quality monitoring conducted from 2008-2010 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 and (2) IDNR/UHL ambient city monitoring downstream from Des Moines near Runnells from 2008 through 2010 (STORET station 10770003).
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supporting" 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" based on results of ambient chemical/physical water quality monitoring. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this assessment segment. The assessments of support of the beneficial uses are based on results of (1) water quality monitoring conducted from 2008-2010 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 and Steffen 2009, Lutz 2010, and Lutz 2011) and (2) IDNR/UHL ambient city monitoring downstream from Des Moines near Runnells from 2008 through 2010 (STORET station 10770003).
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 22 samples collected during the recreational seasons of 2008 through 2010 at IDNR station 10770003 downstream from Des Moines were as follows: the 2008 geometric mean was 377 orgs/100 ml, the 2009 geometric mean was 236 orgs/100 ml and the 2010 geometric mean was 112 orgs/100 ml. The 2008 and 2009 geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml; the 2010 geometric mean is below (meets) the Class A1 criterion. Nine of the 22 samples (41%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.
The geometric means of indicator bacteria (E. coli) in the 27 samples collected during the recreational seasons of 2008 through 2010 at ISU/ACOE station 7 were as follows: the 2008 geometric mean was 387 orgs/100 ml, the 2009 geometric mean was 223 orgs/100 ml and the 2010 geometric mean was 117 orgs/100 ml. All three geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml. Thirteen of the 27 samples (48%) 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 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 conventional parameters (dissolved oxygen, pH, or ammonia-nitrogen) occurred in the approximately 30 samples collected at the IDNR/UHL station during the 2008-2010 assessment period. Also, neither of the two samples analyzed for toxic metals and pesticides exceeded the respective Class B(WW1) criteria. At the ISU/ACOE station, no violations of Class B(WW1) water quality criteria for dissolved oxygen, ammonia, or pH occurred in the 66 samples collected during the 2008-2010 assessment period.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this assessment segment.
