Samples taken from Lincoln Water System’s groundwater-monitoring wells near Ashland show the presence of trace amounts of pesticides, including neonicotinoids commonly used as seed treatments.
The monitoring wells were tested by the U.S. Geological Survey for 151 pesticides in August and September as a precaution, a spokeswoman for Lincoln Transportation and Utilities said, following concerns about potential contamination originating from the troubled AltEn plant.
The biofuel plant south of Mead used treated seed to produce ethanol, leaving behind solid and wastewater byproducts heavily contaminated with agricultural chemicals that flowed into streams and were dumped on fields across Saunders County.
Several streams that received wastewater from AltEn flow southeast to the Platte River near Lincoln’s wellfield.
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The samples, analyzed by the California Water Science Center in Sacramento, detected the presence of five pesticides in the monitoring wells more than a mile from the wells that supply Lincoln with drinking water.
Each of the chemicals detected — herbicides such as atrazine and bentazon, as well as a degraded form of atrazine; azoxystrobin, a fungicide; and clothianidin, an insecticide commonly used in seed treatments — were measured in parts-per trillion, the equivalent of one drop in 500,000 barrels of water.
Clothianidin, which has been found in high concentrations in distiller’s grains and wastewater at AltEn, was detected in one well at 3.7 parts-per trillion, according to the report available on the U.S. Geological Survey’s website.
Lincoln Water System and the U.S. Geological Survey say they believe the sample showing clothianidin was likely influenced by surface water and may not be a reliable indicator of groundwater quality, said Erika Hill, the spokeswoman for Lincoln Transportation and Utilities.
In an email, Hill said there is also nothing to link the chemicals found in the monitoring wells to AltEn, which shut down in February amid mounting violations of state environmental regulations.
“These pesticides are commonly used for agricultural production, therefore, LTU cannot speculate on their origins,†Hill said.
All of the samples measured far below the safety standards set by the Environmental Protection Agency — in some cases more than a million times lower than the benchmark.
With the low levels, Hill said LTU has no plans for further testing of the groundwater-monitoring wells.
"Based on such low-level trace amounts, there is no need at this time," she said.
Other agencies are also monitoring groundwater quality in the Mead area.
The Nebraska Department of Environment and Energy sampled three dozen private drinking water wells for pesticides, nitrates and bacteria in August, discovering pesticides in two downstream from AltEn.
A second sample of the well at the Eastern Nebraska Research and Extension Center immediately south of the ethanol plant showed the level of clothianidin had increased from 0.07 parts-per billion to 0.39 parts-per billion, the department reported.
Environmental regulators also detected small amounts of three pesticides — clothianidin, thiamethoxam and mefenoxam — in a private well 6 miles downstream from the ethanol plant.
All of the levels detected remain well below the human health benchmark for drinking water set by the EPA.
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The presence of chemicals commonly used in agricultural production is nothing new for Lincoln or many municipalities across the state, said Daniel Snow, a research associate professor at the University of Nebraska-Lincoln and director of the Nebraska Water Center.
“There has almost always been low levels of some pesticide residues in Lincoln Water System samples, mainly because the aquifer is in direct connection with the Platte River,†Snow said.
Researchers have monitored the level of atrazine in the Platte River and the connected alluvial aquifer going back as far as the 1980s, Snow said, with studies showing concentrations of the herbicide ebbing and flowing along with rain events.
“What may be new is the number of compounds used in agriculture, though the idea is that they are less toxic and less persistent than older ‘legacy’ pesticides,†Snow added.
The Lower Platte South Natural Resources District, which includes Lincoln and Lancaster County, has detected trace amounts of pesticides in five groundwater samples out of hundreds collected over the last five years, said General Manager Paul Zillig.
Often, the detection of a pesticide will reoccur at the same well, he added.
A more pressing problem for most wells in the area is runoff of fertilizer into groundwater. Last year alone, Lower Platte South NRD detected high levels of nitrates in eight wells.
"The district monitoring wells are often placed in locations that may indicate higher levels of nitrate, so that can skew the data," Zillig said. "But nitrates have consistently been a more widespread and common contaminant than pesticides at this time."