“But to see a really big increase like that, I would suspect it’s some kind of pumping system” that’s causing the increase, he said.

However, if pumping can speed up the movement of a pollution “plume”, the proximity of these wells to a source of pollution is also likely a factor, said Christopher Higgins, professor of civil and environmental engineering at the Colorado School of Mines.

“It’s no surprise that the levels are rising. It is perhaps a little surprising the rate they are increasing, ”said Higgins, whose research focuses on the fate of PFAS in groundwater. “It really has to do with the flow of groundwater and the proximity to where the foam was released, and the fact that chemicals move easily through groundwater.”

The most widely studied PFAS compounds, known as PFOA and PFOS, tend to move at rates “fairly comparable” in groundwater to that of TCE, which moves quite slowly, a. he declares.

But other varieties of PFAS, known as “short-chain compounds,” tend to move faster in groundwater, he said.

They have been used in place of other PFAS compounds in many cases because scientists believe they do not accumulate as much in human and animal tissues as others.

In these cases, PFAS do not adsorb and accumulate on the surfaces of underground soils. “It moves with water. It’s just going faster, ”said Bill Ellett, a retired hydrologist with the Arizona Department of Environmental Quality who now sits on an advisory board that oversees groundwater cleanup on the south side.