Missouri River Water-Quality Monitoring in Relation to Combined Sewer Overflow Systems near Omaha, Nebraska

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In 2012, the USGS Nebraska Water Science Center, in cooperation with the City of Omaha, began monitoring the Missouri River near Omaha to document water-quality changes in the river as the City improved their combined sewer overflow (CSO) system.  The monitoring program includes both discrete and continuous data collection at four sampling sites on the Missouri River. Monitoring at each site includes monthly discrete isokinetic, depth-integrated equal discharge water-quality sampling for nutrients, chlorine, biological oxygen demand, and total suspended solids; cross-sectional profiles of water-quality parameters; Escherichia coli grab samples; measurements of discharge; and continuous monitoring of water-quality parameters.  

In 2012, the USGS Nebraska Water Science Center, in cooperation with the City of Omaha, began monitoring the Missouri River near Omaha to document water-quality changes in the river as the City improved their combined sewer overflow (CSO) system. Omaha’s combined sewer system can overflow into the Missouri River after as little as a tenth of an inch of rain. In support of the City of Omaha's CSO Long-Term Control Plan, the USGS Nebraska Water Science Center is monitoring water quality in the Missouri River with both discrete and continuous data collection. 

Map of water-quality monitoring sites on the Missouri River near Omaha, Nebr.
Water-quality monitoring sites on the Missouri River near Omaha, Nebr. (Public domain.)

Monitoring at each site includes monthly and two yearly rain event discrete isokinetic, depth-integrated equal discharge water-quality sampling for

  • nutrients,
  • bacteria,
  • biological oxygen demand,
  • total suspended solids, and
  • chlorine.

Each discrete water-quality sample collected is classified as wet local or dry local and Missouri River high flow or Missouri River normal flow. 

Continuous Data

Continuous data is collected using water-quality monitors located at three sites along the Missouri River upstream from, in the middle of, and downstream from Omaha.

USGS Nebraska Water Science Center scientists preparing to take a water-quality sample from the Missouri River
USGS Nebraska Water Science Center scientists preparing to take a water-quality sample from the Missouri River near Omaha, Nebr. (Public domain.)

The monitors deployed at each site collect data every 15 minutes for

  • water temperature,
  • specific conductance,
  • dissolved oxygen,
  • pH, and
  • turbidity.

Monitoring Challenges

The monitoring program was designed to address a number of challenges: 

  1. Flows from CSO’s are a very small portion of the larger Missouri River receiving waters being sampled.
  2. Trend detection is difficult because the hydrograph of the Missouri River within a year and between years is so variable.
  3. Contaminates can come from many upstream point and non-point sources which makes detecting what contaminates are coming from the Omaha area and which are coming from upstream sources hard.
  4. Simple grab samples do not represent the actual water quality of the river because the Missouri River is not well mixed.

Data Analysis

Data analysis now is beginning on the three and a half years of monitoring data collected so far.  Information recorded during data collection such as local weather conditions, Missouri River conditions, days since last rain event, and amount of precipitation will be used to classify the data to understand how improvements to the CSO system has affected water quality.
 

Pancake ice on the Missouri River near La Platte, Neb.
Missouri River near La Platte, Nebr. (Public domain.)