October 16, 2011, 3:00 PM. Highway 64, between Barron and Ridgeland, WI.
This video was shot by a family in Western Wisconsin. They were driving down a county road, past a frac sand mine, when they saw this. When new frac sand mines open, there's always a discussion about silica dust, because it's a carcinogen. Mine developers are usually quick to point out that dust isn't ever a public health problem, because the sand is either kept contained or kept wet, or both.