Missouri River IA 06-WEM-1709

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 20 samples collected during the recreational seasons of 2012 through 2014 at Missouri River near Council Bluffs (station 06610505) were as follows: the 2012 geometric mean was 92 orgs/100 ml, the 2013 geometric mean was 188 orgs/100 ml, and the 2014 geometric mean was 423 orgs/100 ml. Two of the three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Eight of the combined 20 samples (40%) 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). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as "partially supported".

The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" (IR Category 4c, non-pollutant stressor) based on the assessment developed for previous reporting cycles (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. As they have in all previous assessment periods, results of ambient water quality monitoring conducted by USGS during the 2010-2014 assessment period, however, suggest good water quality in this river segment. No violations of Class B(WW1) criteria occurred in the samples analyzed during this period for ammonia (38 samples, maximum of 0.35 mg/l), dissolved oxygen (48 samples, minimum = 6.0 mg/L), pH (47 samples, range from 8.0 to 8.7 pH units), chloride (38 samples), or sulfate (38 samples). No violations of the Class B(WW1) criterion for temperature occurred in the 323 samples collected during the 2010-12 period. Levels of toxic metals (e.g., arsenic and selenium) and pesticides (e.g., chlorpyrifos and dieldrin) in the 36 samples collected were below their respective Class B(WW1) criteria.

Iowa DNR’s previous assessments of support of the Class C (drinking water) uses in this river segment were based on violations of the state human health water quality criterion for arsenic (includes contributions of arsenic from consuming fish as well as from drinking water). Monitoring data from USGS station 06610000 at Omaha have shown that levels of arsenic in this river segment average between 2 and 3 ug/l, thus far exceeding Iowa’s human health criterion (fish + water) of 0.18 u g/l. For the recent (2010-12) period, arsenic levels in the 37 samples collected ranged from 1.5 to 4.6 ug/l, with a mean level of 2.5 ug/l; all samples exceeded Iowa’s human health criterion. These results are consistent with results of past monitoring periods with mean levels of arsenic over the last 12 years (2000-2012) ranging from 2.3 to 2.6 ug/l (from 31 to 45 samples analyzed per assessment period) and with 100% of the samples analyzed in violation of the HH criterion of 0.18 ug/l. Iowa DNR has incorrectly identified impairments of the drinking water use by comparing USGS data for dissolved arsenic to Iowa’s water quality criterion for arsenic III. Results of monitoring data for arsenic III would be needed in order to identify violations of Iowa’s Human Health criterion for arsenic III: these data do not exist. Thus, this impairment was de-listed for the current 2014 Integrated Reporting cycle.

Levels of nitrate (maximum of 5.6 mg/l; average = 1.05 mg/l) during the 2012-2014 monitoring period were well-below the Class C water quality criterion of 10 mg/l as N. Pesticide monitoring at USGS station 06610000 was terminated in October 2012; thus, the data summary from the 2010-2012 monitoring period remains the most recent available. During that monitoring period, the average level of atrazine in the 40 samples collected was 0.3 ug/l (maximum 2.0 ug/l). Levels of alachlor in the 36 samples collected were very low with a maximum level (the only detectable level) of 0.024 ug/l; all other values were <0.008 ug/l. Levels of both atrazine and alachlor were far below their respective Class C human health criteria of 3 and 2 ppb. Based on DNR's Section 305(b) assessment methodology, if the average contaminant level in source water is less than the MCL, the Class C (drinking water) uses of the source water should be assessed as "fully supported."

Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.