Assessment Comments
Assessment is 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, (2) IDNR/SHL ambient city monitoring downstream from Des Moines near Runnells from 2010 through 2012 (STORET station 10770003) and (3) IDNR/SHL biological sampling conducted in 2012.
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 (evaluated) as "not supported" (IR 3b-u) based on the results of the 2012 IDNR/SHL biological sampling. Fish consumption uses remain "not assessed" (IR 3a) 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 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) 2012 IDNR/SHL biological sampling.
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/SHL 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/SHL 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.
In contrast to the water quality aquatic life assessment, the aquatic life assessment based on biological sampling suggests the aquatic life uses are "partially supporting". This evaluated biological assessment was based on data collected in 2012 as part of the IDNR/SHL large river sampling project. A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa collected in the stream sampling reach. The biological metrics were combined a benthic macroinvertebrate index (BMIBI). The index rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2012 BMIBI score was 13 (poor). The aquatic life use support was assessed (evaluated) as not supporting (=NS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008. The BMIBI BIC for this ecoregion is 51. This assessment is considered evaluated because the drainage area (11,655 mi2) above this sampling site was far greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site failed the BMIBI BIC (0/1), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size. According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this assessment segment.
