Assessment Comments
Assessment is based on (1) surveys of Nebraska fisheries biologists and consultation with IDNR staff, (2) ambient monitoring by Nebraska DEQ in 2000, (3) 2006 assessment information from Nebraska DEQ, and (4) results of USGS/NASQAN water quality monitoring at Omaha (I-80 bridge) from 2002-04.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as “not supported” based on the impairment identified by the Nebraska DEQ due to high levels of indicator bacteria. The Class B(WW) 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 remain 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 2002 through December 2004 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) 2006 assessment information from Nebraska DEQ.
EXPLANATION: The Class A (primary contact recreation) uses remain assessed (monitored) as "not supported"; this is the same assessment as that developed for Iowa’s 2002 and 2004 Section 305(b) reporting cycles. See narratives for either of these assessments for details regarding this impairment. This impairment is based on the impairment of primary contact recreation uses identified for this segment of the Missouri River by the Nebraska Department of Environmental Quality for the 2006 Section 303(d) listing cycle. The Nebraska DEQ identified an impairment of primary contact recreation uses in this river segment due to high levels of indicator bacteria.
The Class B(WW) uses remain assessed (evaluated) as "partially supported" based on the assessment developed for the 1998 and 2000 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 USGS monitoring at the Omaha station during the 2002-2004 assessment period continue to suggest relatively good water quality for support of aquatic life uses. Levels of pH, dissolved oxygen, ammonia-nitrogen were all below Class B(WW) criteria in the 45 samples collected. Levels of pH ranged from 8.7 to 7.7, the minimum dissolved oxygen level was 5.2 mg/l, and the maximum level of ammonia-nitrogen was 0.39 mg/l. None of the 45 samples collected during the 2002-2004 period violated Class B(WW) water quality criteria. Levels of pesticides (for example, DDT, dieldrin, chlorpyrifos, lindane, and parathion) were all below their respective Class B(WW) criteria in the 45 samples analyzed during the 2002-2004 assessment period. For the 1998-1999 305(b) reporting cycle, levels of dieldrin exceeded Class B(WW) criteria in two of the 29 samples collected during the 1998-1999 biennial period (thus suggesting "partial support" of aquatic life uses). During the 2000-2002 period, levels of dieldrin levels were below levels of detection in all 31 samples collected. This pattern continued during the 2002-2004 period with levels of dieldrin in all 45 samples collected (levels of detection ranged from 0.005 to 0.009 ug/l).
Similar to previous assessments for this river reach, the Class C (drinking water) uses remain assessed as "not supported" due to violations of the state human health water quality criterion for arsenic. Violations of Iowa’s human health criterion for arsenic (0.18 ug/l) occurred in all 45 samples (100% violation) collected during the 2002-2004 assessment period. Arsenic levels ranged from 1.7 to 2.9 ug/l, with a mean level of 2.3 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 2002-2004 period (2.3 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 45 samples collected from the Omaha station during the 2002-2004 assessment period. The maximum level of nitrate was 2.6 mg/l. Regarding atrazine, however, three of the 45 samples, however, contained atrazine above the MCL of 3 ug/l. The mean level of atrazine in the combined 45 samples collected from the Missouri River from 2002 through 2004 (0.7 ug/l) was well-below the MCL of 3 ug/l. None of the 45 moving annual averages for atrazine for the years 2001 through 2004 exceeded the MCL (maximum average = 1.2 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 criteria.
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.
