Des Moines River IA 04-LDM-1020
upper end of Red Rock Reservoir (W line S34 T77N R20W Marion Co.) to confluence with South R. in S12 T77N R22W Warren Co.
- Cycle
- 2018
- Release Status
- Final
- Overall IR
- 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
- Trend
- Unknown
- Created
- 5/29/2019 10:05:40 AM
- Updated
- 8/1/2019 2:51:45 PM
The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supporting" due to levels of indicator bacteria (E. coli) that slightly exceed state water quality standards. The Class B(WW1) aquatic life uses are assessed (evaluated) as "partially supported" based on the results of the 2012 and 2013 DNR/SHL biological sampling. 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 2014-2016 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) DNR/SHL ambient city monitoring downstream from Des Moines near Runnells from 2014 (STORET station 10770003) and (3) 2012/2013 DNR/SHL biological sampling.
Note: A TMDL for bacteria was prepared by DNR and approved by U.S. EPA in March 2010. Because this TMDL covers all the identified impairments for the assessment segment, this segment was moved to IR Category 4a (TMDL approved). The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 41 samples collected during the recreational seasons of 2014 through 2016 ISU/ACOE Station 7 (17770003) at County Road S35 near Runnells were as follows: the 2014 geometric mean was 284 orgs/100 ml, the 2015 geometric mean was 357 orgs/100 ml, and the 2016 geometric mean was 162 orgs/100 ml. All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Nineteen of the combined 41 samples (46%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Samples collected during the recreational seasons of 2014 at DNR station 10770003 downstream from Des Moines were as follows: the 2014 geometric mean was 523 orgs/100 and Four of the combined 6 samples (67%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml.Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as "partially supported." Results from both the ISU/ACOE and DNR/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 9 samples collected at the DNR station during the 2014 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 58 samples collected during the 2014-2016 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 and 2013 as part of the DNR/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) and the 2013 BMIBI score was 34 (fair). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), 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 (0/2), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the site used for the assessment doesn’t fall in the calibrated watershed size. According to DNR’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). DNR 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.