THE INNOVATORS
Removing Nitrates From Groundwater via Wood Chip Walls
L
ike many agricultural regions in the United States, New Zealand’s South Island deals with the contamination of its groundwater by nitrates. However, the situation is distinct in two respects. First, the alluvial gravel aquifers that underlie much of the intensively farmed land on New Zealand’s South Island are extremely permeable and are characterized by fast groundwater velocities. Second, the primary source of nitrogen in the groundwater is the waste produced by New Zealand’s millions of dairy cows. In this interview, Lee Burbery, a scientist at the Institute of Environmental Science and Research (ESR) in Christchurch, speaks with Irrigation Leader about the technical, political, and economic challenges of combatting nitrate pollution and about the wood chip denitrification wall installations he is researching. Irrigation Leader: Please tell us about your background and how you came to be in your current position.
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the development of a recirculating tracer well test concept, which was a means by which nitrate reduction rates might be measured in situ in fast-flowing aquifers where single-well push-pull tests were impracticable. From 2008 to 2010, I did a stint as a hydrogeologist for the local regional council before returning to groundwater research. Seven years ago, I started working as a senior groundwater scientist at ESR, which is one of several government-owned science research entities referred to in New Zealand as Crown Research Institutes. The fate and transport of pathogens and nitrate in New Zealand groundwater systems are two of my major research themes. For many years I worked on projects aimed at evaluating the capacity of various New Zealand groundwater systems to assimilate nitrate pollution from intensive land use. More recently, this has bent toward the research and development of possible nitrate mitigation and groundwater nitrate remediation options. Since alluvial gravel aquifers typify New
Zealand hydrogeology, they are the systems I am most interested in. Irrigation Leader: Please tell us about the nitrate issue in New Zealand. Lee Burbery: Agriculture has long been a mainstay of the New Zealand economy, and agriculture and nitrate pollution go hand in hand. Since the 1990s, however, agricultural land use in New Zealand has intensified significantly thanks to advances in irrigation, especially the use of groundwater pumped from highyielding alluvial gravel aquifers. Driving this has been the massive expansion of the dairy industry. Accounting for 3.1 percent of gross domestic product, dairying now ranks as the fifth-largest industry in New Zealand. The national dairy herd is now 6.4 million cows— outnumbering the human population of 4.8 million. When you consider that a cow produces about 20 times more waste than a human, you can start to appreciate the scale of the agricultural waste problem on the small islands of New Zealand.
PHOTO COURTESY OF LEE BURBERY.
Lee Burbery: After graduating with an environmental science degree from Lancaster University in the United Kingdom in 1996, I worked as an environmental consultant with the company ARCADIS Geraghty & Miller International, Inc. Most of my work involved conducting contaminated site investigations and toxicological risk assessments. In 2000, I returned to Lancaster to complete a PhD. My thesis concerned the limitations of single-well push-pull tests for measurement of in situ biodegradation rates in groundwater. At the time, monitored natural attenuation was developing as an approved groundwater remediation strategy and push-pull tests were evolving a conventional fieldtesting method. In 2005, I moved to New Zealand to conduct postdoctoral research on
A wood chip barrier installation.
