Missouri River IA 06-WEM-1722

The Class A1 (primary contact recreation) uses are assessed as "partially supporting" based on the bacterial impairment identified for this assessment segment by the state of Nebraska. A TMDL for the Nebraska impairment in this segment of the Missouri River was approved by EPA in 2007. Because Iowa DNR did not participate in the preparation of this TMDL, this impairment is appropriate for Category 5a of Iowa's Integrated Report.

The Class B(WW1) uses remain assessed (evaluated) as "partially supported" (IR Category 4c, non-pollutant stressor) based on the assessment developed for the 1998, 2000, and 2002 reports (i.e., habitat alterations and flow modifications that resulted from development of the river for navigation uses in the mid-Twentieth Century). This assessment was developed in consultation with the Missouri River fisheries biologist for the state of Nebraska. Although parameter coverage is limited, results of ambient water quality monitoring by USGS from June 2011 to August 2012 at Sioux City do not suggest water quality problems in this segment of river. No violations of Class B(WW1) criteria occurred in the 13 samples analyzed for dissolved oxygen (minimum = 7.4 mg/l) or in the 14 samples analyzed for pH (range: 8 to 8.5 pH units). None of the 230 samples measured for water temperature exceeded the Class B(WW1) criterion of 32C (maximum = 30.7C).

Fish consumption uses remain assessed (monitored) as “fully supported” based on results of U.S.EPA/DNR fish contaminant monitoring near Sergeant Bluff in 2012, 2013 and 2015. The composite samples of fillets from paddlefish collected in 2012 had low levels of contaminants. Levels of primary contaminants in the four-fish composite sample of paddlefish fillets in 2012 were as follows: mercury: 0.091 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm.

Results from fish contaminant monitoring in 2013 showed low levels of contaminants in the composite sample of channel catfish fillets: mercury: 0.11 ppm, chlordane: <0.2 ppm, and total PCBs (levels of Aroclors 1248, 1254, and 1260 were all below the level of detection of 0.2 ppm). The average level of mercury in five flathead catfish, however, was 0.301 ppm (SD = 0.108 ppm). The 2013 average mercury level was just over (above) the Iowa DNR/Iowa Dept. of Public Health threshold for a one meal per week consumption advisory of 0.300 ppm.

According to the Iowa DNR/Iowa Dept. of Public Health fish advisory protocol, the single occurrence of contaminant above an advisory trigger level does not typically result in issuance of an advisory. Such an advisory is issued only after follow-up monitoring confirms that contaminant levels exceed the advisory trigger level. Thus, follow-up monitoring was conducted in 2015 in this river segment as part of the Iowa DNR’s fish tissue monitoring program to better define the level of mercury in flathead catfish fish. Results of this 2015 follow-up monitoring showed very low levels of mercury. The average level of mercury in the tissue plugs from five flathead catfish was 0.08 ppm (SD = 0.041 ppm) which is well below the consumption advisory threshold of 0.3 ppm.

The fish contaminant data generated from the 2012, 2013 and 2015 Iowa DNR sampling conducted in this river segment show that the levels of contaminants are generally low and do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.