Scientists can trace contamination in Yakima Valley wells

Federal scientists have developed a new tool that can trace contaminated water found in Yakima Valley wells back to its general source area, the U.S. Geological Survey announced on Wednesday.

The new computer model, based on an existing system that tracks Yakima River Basin groundwater, could determine the origin of nitrates responsible for contaminating 10 to 20 percent of private wells in the Lower Valley.

Unknown, however, is whether the model will be used by the committee tasked with reducing nitrates in the Lower Valley’s groundwater.

So far the committee — known as the Groundwater Management Area Committee, or GWMA for short — has been careful to avoid identifying site-specific sources of the pollution, which is linked to commercial fertilizers, dairy manure, and leaking septic systems.

“This doesn’t identify sources in terms of land uses, it looks at where the water moves in what time frame,” said the Geological Survey’s lead scientist, Matt Bachmann. “I know it’s a politically contentious issue, so how this gets used is up to the people that want to use it.”

More than a year ago, the GWMA turned down an offer from the Geological Survey to develop a model that would track how nitrates move from sources to drinking water wells, where elevated levels pose a serious health risk to infants and pregnant women.

That decision was based in part on funding — the USGS wanted $300,000 in matching funds for the study — and in part on the committee’s desire to focus on other research first, said Vern Redifer, public services director for Yakima County, which is managing the GWMA.

Agricultural industry representatives on the GWMA were also wary of the idea because it could potentially be used to blame specific landowners and put them at risk of lawsuits.

The model unveiled this week is different from the one the agency proposed to the GWMA because it tracks the movement of water rather than the containments in the water.

But this model, which was started before the agency proposed a specific nitrate tracking model, can be used to answer similar questions about where contamination is coming from.

“There’s a slight difference between the areas contributing water to wells and areas contributing nitrate, but it’s not too different, it’s still centered in the same area,” Bachmann said. “This is the best estimate we have for where the particles in those wells came from.”

The model tracks the water’s path from each well back to the surface where it started as rain, snow, or irrigation. Well, approximately. The model uses 1,000-foot-square units, Bachmann said.

Groundwater movement varies with depth and geology. But in general a study based on data from the new model found that the water in most of the valley’s shallow wells was coming from an average of three miles away, in most cases taking about three years. For some deeper wells, the water took decades to move along its path from the surface to the well.

The report doesn’t attempt to pinpoint all sources of nitrate in the Lower Valley, only the sources of water for the 121 contaminated wells studied by the Environmental Protection Agency in 2011, Bachmann said.

“We only looked at a small number of wells, but it’s a tool anyone can use to track water from other wells,” he said.

Bachmann hopes the GWMA will be able to use this tool, but his recent offer to present his research to the committee was turned down, he said.

Redifer said the committee decided last week to have its data work group evaluate the study before inviting Bachmann to present his findings.

“There’s interest, but we need to know what it does, how it works, and its practicality,” Redifer said. “It might serve a very useful purpose, but the (committee) decided that we need to know more first.”

The Environmental Protection Agency provided funding and data toward the Geologic Survey’s study. EPA spokesman Mark MacIntyre said while he couldn’t speak for the GWMA, he expects the study to be useful in addressing the Lower Valley’s nitrate problem.

“We know it’s going to help us get to where we all want to be, which is protecting people’s health in the valley and a really important groundwater resource,” MacIntyre said. “We just welcome all good science.”

This story was originally published October 21, 2015 at 10:03 PM with the headline "Scientists can trace contamination in Yakima Valley wells."