Assessment Comments
Assessment is based on: (1) results of monitoring conducted from February 2004 through December 2006 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 February 2004 through December 2006 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/).
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. This assessment represents a de-listing of Iowa’s 2006 bacteria impairment for this assessment segment. The rationale for this delisting is as follows. The NDEQ had identified an impairment of primary contact recreation uses in this river segment (NDEQ segment MT1-10000) for the 2004 listing cycle due to high levels of indicator bacteria (fecal coliforms). Based on this information, Iowa DNR included this segment on its 2004 Section 303(d) list. Based on incorrect information in a draft version of Nebraska’s 2006 Integrated Report, Iowa DNR mistakenly retained this impairment on its 2006 Section 303(d) list. According to staff of the Nebraska DEQ, however, this impairment was de-listed during Nebraska’s 2006 Integrated Reporting cycle: samples of E. coli collected from this segment of the Missouri River in 2005 yielded a recreation season geometric mean of 72 orgs/100 ml (N=22), indicating that the bacterial impairment should be de-listed. Nebraska’s 2008 Integrated Report also shows that recreation uses for Missouri River segment MT1-10000 are fully supported. Thus Iowa DNR is de-listing this impairment for the current (2008) Integrated Reporting cycle.
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 2004-2006 assessment period, however, suggest good water quality in this river segment. No violations of Class B(WW1) criteria occurred in the 42 samples analyzed during this period for ammonia (maximum of 0.4 mg/l) or pH (range from 7.7 to 8.7 pH units). Levels of toxic metals (e.g., selenium and arsenic) and pesticides (e.g., dieldrin and DDE) in the 42 samples collected were below their respective Class B(WW1) criteria. One of 41 samples violated the Class B(WW1) criterion for dissolved oxygen: the sample collected on June 28, 2005 contained 4.9 mg/l, thus slightly violating the Class B(WW1) criterion of 5.0 mg/l. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), however, the percentage of violations at this station during the 2004-2006 period for dissolved oxygen (2%) does not suggest a water quality impairment. These guidelines allow up to 10% violations of conventional parameters such as dissolved oxygen, pH, and water temperature before impairment of water quality is indicated.
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 42 samples (100% violation) collected during the 2004-2006 assessment period. Arsenic levels ranged from 0.2 to 6.2 ug/l, with a mean level of 2.35 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 2004-2006 period (2.35 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 42 samples collected from the Omaha station during the 2004-2006 assessment period. The maximum level of nitrate was 5.5 mg/l in the sample collected on May 5, 2006. Regarding atrazine, one of the 42 samples contained atrazine above the MCL of 3 ug/l: the sample collected on May 14, 2005 contained 7.5 ppb of atrazine. The mean level of atrazine in the combined 42 samples collected from the Missouri River from 2004 through 2006 (0.5 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 (fish plus water) criteria.
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.
