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/IDNR fish contaminant (RAFT) monitoring near Sergeant Bluff in 2004, 2007, 2012, 2013, and 2015.  Levels of primary contaminants in the composite sample of common carp fillets in 2004 were as follows: mercury: 0.101 ppm; total PCBs: 0.09 ppm; and technical chlordane: 0.043 ppm.  Levels of primary contaminants in the composite sample of flathead catfish fillets in 2004 were as follows: mercury: 0.062 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.  Follow-up sampling conducted in 2007 showed that levels of primary contaminants in the composite sample of freshwater drum fillets were as follows: mercury: 0.195 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm.  The composite samples of fillets from paddlefish collected in 2012 also had low levels of contaminants.  Levels of primary contaminants in the four-fish composite sample of paddlefish fillets in 2012 were as follows: mercury:  0.0906 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 (standard deviation = 0.108 ppm; maximum = 0.426 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 this river segment in 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 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 (standard deviation = 0.041 ppm; maximum = 0.13 ppm) which is well below the consumption advisory threshold of 0.300 ppm. 

The fish contaminant data generated from the 2004, 2007, and 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.