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GROUNDWATER NITRATE INVESTIGATION PROJECT

Lower Platte South Natural Resources District
Lincoln, Nebraska

 

EA conducted groundwater nitrate verification studies that investigated the spatial distribution, source, and transport of nitrate contamination in eight Community Water System Protection Areas (CWSPAs) located within the Lower Platte South Natural Resources District (LPSNRD) of Nebraska. The CWSPAs investigated include Weeping Water, Davey, Elmwood, Hickman, Otoe Co. RWD#3, Pleasant Dale, Sprague, and Union.

Previous sampling results from municipal wells in the CWSPAs had found nitrate levels at some monitoring locations above the LPSNRD Phase II (5.0 parts per million [ppm]) and Phase III (8.0 ppm) triggers. The Maximum Contaminant Level for nitrate, from the National Primary Drinking Water Regulations list, is 10 ppm. The elevated nitrate levels are threatening the drinking water supply, and alternative sources of drinking water will be extremely costly.

The LPSNRD requires that the sources of nitrate be verified before a Phase II or Phase III nitrogen management area is declared. The purpose of the studies was to identify the sources and extent of the reported nitrate within all eight CWSPAs.

Hollow-stem auger rig
Hollow-stem auger rig with a continuous core sampler used to determine geologic conditions, collect soil samples, and install monitoring wells; most of the drilling was completed during the winter to minimize disruption to land owners

The studies involved inventories and assessments of available information; installation of 27 groundwater monitoring wells; and collection and analyses of hundreds of shallow soil, subsurface soil, and groundwater samples.

The results of the studies show an extensive amount of leachable nitrate in the soil within the study areas, and the potential for large amounts of nitrate to be leached into the groundwater. Agricultural management practices can be used to reduce the amount of nitrate leached from within the root zone in the future; however, the magnitude of the existing subsoil contamination beneath the root zone is certain to continue to add to the level of nitrate in the aquifer.

EA presented the results of the studies at Town Council Meetings. The studies were initiated in 2006, completed in 2009, and performed under budget. In February 2011, EA earned a 2011 Engineering Excellence Merit Award, under the Small Projects category, from the American Council of Engineering Companies—Nebraska (ACEC/Nebraska) for this project. Awards

 

Lower Platte South Natural Resources District
From left to right: Jim Wathen, EA Senior Engineer; Adrian Smith, U.S. Congressman; Doug Samuelson, Director, LPSNRD; Dan Schulz, LPSNRD; Dale Schlautman, EA Lincoln Office Manager; Tom O’Connor, Nebraska Department of Natural Resources; and Marty Wiedenman, ACEC/Nebraska President.