Assessment Comments
Assessment is based on: (1) results of monitoring conducted from January 2006 through December 2008 by the U.S. Geological Survey at station 06610000 at Omaha (part of the USGS NASQAN monitoring network), (2) information from Nebraska fisheries biologists, and (3) assessment information from Nebraska DEQ’s 2008 Integrated Report (http://www.deq.state.ne.us/).
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “fully supported” based on data and information from the Nebraska DEQ. The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" based on information from local fisheries biologists on impacts related to flow modification and habitat alterations in this segment of the Missouri River. The Class C (drinking water) uses are assessed (monitored) as "not supported" due to levels of arsenic that exceed state water quality criteria to protect human health from arsenic in fish and water. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment. Sources of data for this assessment include (1) results of monitoring conducted from January 2006 through December 2008 by the U.S. Geological Survey at station 06610000 at Omaha (part of the USGS NASQAN monitoring network), (2) information from Nebraska fisheries biologists, and (3) assessment information from Nebraska DEQ’s 2008 Integrated Report (http://www.deq.state.ne.us/). [Note: Nebraska's 2010 Integrated Report was not yet available during development of this (2010) assessment.]
EXPLANATION: The Class A1 (primary contact recreation) uses are assessed (monitored) as “fully supported” based on the assessment of primary contact recreation uses identified for this segment of the Missouri River by the Nebraska Department of Environmental Quality (NDEQ) for their 2006 and 2008 Section 303(d) listing cycles.
The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" 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. Results of ambient water quality monitoring conducted by USGS during the 2006-2008 assessment period, however, suggest good water quality in this river segment. No violations of Class B(WW1) criteria occurred in the 37 samples analyzed during this period for ammonia (maximum of 0.78 mg/l), dissolved oxygen (minimum = 5.7 mg/L) or pH (range from 7.7 to 8.6 pH units). Levels of toxic metals (e.g., selenium and arsenic) and pesticides (e.g., dieldrin and DDE) in the 37 samples collected were below their respective Class B(WW1) criteria.
Similar to previous assessments for this river reach, the Class C (drinking water) uses remain assessed (monitored) as "not supported" due to violations of the state human health water quality criterion for arsenic (includes contributions of arsenic from consuming fish as well as from drinking water). Violations of Iowa’s human health criterion for arsenic (0.18 ug/l; fish plus water) occurred in all 37 samples (100% violation) collected during the 2006-2008 assessment period. Arsenic levels ranged from 1.6 to 4.1 ug/l, with a mean level of 2.60 ug/l. According to IDNR guidelines for Section 305(b) assessments, if the mean level of a toxic metal or pesticide is greater than an MCL or human health criterion, "nonsupport" of the drinking water use is indicated. The mean level of arsenic during the 2006-2008 period (2.60 ug/l) is well above the human health criterion of 0.18 ug/l; thus, continued “nonsupport” of drinking water uses is indicated. Levels of nitrate, alachlor, cyanazine, and toxic metals were well below their respective Class C human health criteria, MCLs and/or MCLGs in the 37 samples collected from the Omaha station during the 2006-2008 assessment period. The maximum level of nitrate was 5.5 mg/l in samples collected on May 5, 2006 and June 16, 2008. Regarding atrazine, one of the 37 samples contained atrazine above the MCL of 3 ug/l: the sample collected on March 7, 2006 contained 3.8 ppb of atrazine. The mean level of atrazine in the combined 37 samples collected from the Missouri River from 2006 through 2008 (0.3 ug/l) is well-below the MCL of 3 ug/l. 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." The overall assessment for Class C (drinking water) uses, however, remains “not supported” (monitored) due to levels of arsenic that exceed Class C (i.e., Human Health (fish plus water)) criteria.
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.
