EAST PALESTINE, Ohio (WJW) — Amid skepticism about the safety of the village’s water supply following a train derailment that spilled toxic chemicals, state officials on Tuesday explained the water sampling process that’s continuing at the village’s water treatment plant.

Tuesday’s sampling work was the fourth round of water testing done at the village’s five municipal wells since the Feb. 3 derailment, which led to a fire and a controlled burn of vinyl chloride to avoid a potentially catastrophic explosion.

“We wanted everyone to understand what goes into these samples,” said Amy Klei, chief of the Ohio EPA’s Division of Drinking and Ground Water. “There’s a lot of quality control steps to ensure the integrity of these samples.”

Workers from the village and an outside contractor, AECOM, were seen Tuesday measuring factors like acidity, conductivity and dissolved oxygen, then comparing their data points to make sure they match. At the village’s private drinking wells, the Columbiana County Health District is also assisting with water testing, Klei said.

The village’s treatment plant draws from five wells, encased in steel and ranging in depth from 60 feet to nearly 100 feet — deeper than the village’s private wells, some of which may be at-risk, officials have said.

“Protecting this source water and getting as much information on what’s coming into the village’s treatment plant is a top priority for us,” Klei said.

To that end, new monitoring wells — called “sentinel” wells — placed uphill from the plant between it and the crash site are expected to give advance warning of contaminants moving toward the municipal wellfield. Those wells are expected to be tested for the first time later this week, she said.

So far, testing of the five wells’ raw and treated water has not shown any evidence of contamination from the derailment, Klei said.

“It doesn’t mean we’re walking away. If we see threats or we start to see detections, we are working on contingency plans with the village,” she said.

It’s currently unclear how often the village’s municipal water supply could be tested. Right now, it’s once a week at minimum, Klei said.