March 29, 2007
The Missoulian reports that water quality monitoring in Milltown shows a dramatic drop in arsenic levels in some monitoring wells. One well that tested last summer at 339 parts per billion (ppb) arsenic had dropped to just under 18 ppb. The federal standard for groundwater arsenic is 10 ppb. Reclaiming the Milltown aquifer is the primary goal of the Milltown cleanup.
The precipitous decline is likely attributable, in part, to the draw down of the reservoir and the consequent removal of the hydraulic head believed to cause leaching of arsenic into the aquifer.
“The drop in arsenic levels in our monitoring wells was something we expected to see,” said the EPA’s Russ Forba in the Missoulian article. “When the river levels come up this spring, we may see arsenic levels in the wells increase some.”