Missouri River IA 06-WEM-1708

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 53 samples collected during the recreational seasons of 2014 through 2016 at Missouri River near Council Bluffs (station 06610505) were as follows: the 2014 geometric mean was 295 orgs/100 ml, the 2015 geometric mean was 368 orgs/100 ml, and the 2016 geometric mean was 324 orgs/100 ml. All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Twenty Seven of the combined 53 samples (51%) 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 Iowa 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). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as "partially supported."

Results of chemical/physical water quality monitoring at Missouri River near Council Bluffs (station 06610505) suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW1) water quality criteria for 16 Ammonia samples (maximum = 0.2 mg/L), 76 pH samples (range = 7.7 to 8.5), or 76 Temperature samples (maximum = 28.7°C) occurred during monitoring from January 2014 to December 2016. Two of the 76 samples (3%) analyzed for Dissolved Oxygen (minimum = 4.5 mg/L) violated the Class B(WW1) criteria during the 2014-2016 monitoring period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17) and Iowa DNR's assessment/listing methodology, a violation frequency of significantly greater than 10% for conventional parameters such as Dissolved Oxygen suggests impairment of aquatic life uses. Because the frequency of violations for this parameter is not greater than 10 percent, these results do not suggest impairment of the Class B(WW1) aquatic life uses.

Fish consumption uses are assessed (monitored) as “fully supported” based on results of DNR fish contaminant monitoring south of Council Bluffs in 2013, 2014 and 2016. Levels of primary contaminants in the 2013 composite sample of channel catfish fillets were as follows: mercury: 0.13 ppm; total PCBs: <0.6 ppm; and technical chlordane: <0.2 ppm. The average level of mercury in the 2013 tissue plug samples from four flathead catfish was 0.247 ppm (SD = 0.030). The average level of mercury in the 2015 tissue plug samples from three flathead catfish was 0.090 ppm (SD = 0.069). Levels of primary contaminants in the 2016 composite sample of whole common carp were as follows: mercury: 0.05 ppm; total PCBs: <0.06 ppm; and technical chlordane: 0.05 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. The results of fish contaminant monitoring in this assessment segment from the 2013, 2014 and 2016 sampling, however, show that the levels of contaminants do not exceed any of Iowa' advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.