Stimulating natural microorganisms that reduce nitrates in groundwater could help some communities put restricted water wells back in use.

Roy Spalding, a University of Nebraska hydrochemist, and Imtiyaz Khan, a sanitary engineer, are refining an inexpensive, sustainable technique that small utilities could use to reduce or eliminate nitrate from water supplies.

The safe limit for nitrates in drinking water is 10 parts per million. Higher concentrations pose health risks to infants and pregnant women and have been linked to some cancers. Nitrate contamination is the most pervasive shallow groundwater contamination problem in the Upper Midwest, Spalding said.

This NU Institute of Agriculture and Natural Resources team modified an existing technique to use pulsed injections of ethanol or acetate into contaminated wells. The pulsed injections make the process sustainable, Spalding said.

Ethanol and acetate stimulate natural microbes that convert nitrates into innocuous nitrogen gas and biodegrade into harmless carbon dioxide.

The process, called a daisy well system, involves installing injection and extraction wells in a circular pattern around a contaminated well. A computer times the pulsed injections of ethanol or acetate and nitrate-free water into the groundwater. As the groundwater moves through the system, it is treated and the resulting extraction well water is cleaned of nitrates.

"This is a first, a pilot project, that we hope will one day change how public water systems treat nitrates," Spalding said. Spalding and Kahn have extensively tested and modified the daisy well system over the past several years at several locations across Nebraska, including in Merrick County near Central City.

Their refined system effectively reduces nitrates to acceptable levels in a short time, Spalding said.

– Steve Ress