The amounts of nitrates leaching into groundwater beneath the city of Hastings are approaching levels that could result in serious health effects for very young infants, officials said, reviving calls to build a new water treatment facility.

Several months after the city released results of a survey of nitrate contamination in its six wells, Dakota County came out with a study showing that almost a third of private wells in the county had elevated levels of the nitrogen-based compound derived from agricultural fertilizers and livestock waste.

Two of the city’s wells had levels of nitrates in the range of “the high 7s and low 8s,” said Hastings Public Works Director Tom Montgomery. The current standards recommended by the U.S. Environmental Protection Agency limit nitrates to a total of 10-milligram-per-liter, or parts per million.

The findings from the county study showed that 226 of the 742 private wells tested exceeded federal drinking-water quality standards, agriculture officials said.

Researchers say there is strong evidence that exposure to nitrates can pose serious health risks for infants under six months and pregnant women. Hastings’ wells aren’t at that level yet, but there is fear that they could pass the threshold.

The potential health risks are well known to local officials.

Montgomery, the public works director, said the city, which has already spent millions of dollars to install sophisticated water treatment equipment, is considering reviving plans to build a new $2.5 million water plant near two of the affected wells.

The project was first proposed several years ago, said Jill Trescott, Dakota County’s groundwater-protection supervisor, when the city’s population was climbing steadily and officials were looking to modernize its water system. But residential growth stalled, and the plan was mothballed, she said.

“Both with the high nitrates that are in the city’s drinking water wells and also with the private wells that are in the surrounding communities, there’s quite a serious issue with nitrate that’s over the drinking water standard,” Trescott said.

In a recent follow-up study, also funded by the Minnesota Department of Agriculture, county officials tested 667 private wells in the cities of Hastings, Coates and Hampton and the townships of Castle Rock, Douglas, Hampton, Marshan, Nininger, Randolph, Sciota, Vermillion and Waterford, according to Kimberly Kaiser, a hydrologist with the Agriculture Department. She said the results of that study, which will be released soon, will help the agency formulate better fertilizer-management practices for farmers.

“We’ve seen that farmers in the county have been making strides in changing their fertilizer practices to be more efficient with it so that it wastes less, and so that less goes into the water, but unfortunately they’re going to have to do more so that less of the nitrates get into the water,” Trescott said.

Though plants absorb some of the nitrates from fertilizer, most of it leaches into the groundwater, Trescott said.

“Hastings and the area around there has many sandy soils where water can flow through quickly,” said Randy Ellingboe, manager of the Minnesota Department of Health’s Drinking Water Protection Section, which is charged with enforcing federal drinking-water standards. “As water moves through the sand or gravel layers, it may then become part of the groundwater that serves as an aquifer for Hastings.”