MINNEAPOLIS (AP) _ Officials in Wisconsin are testing the environmental and health impacts following a frack sand sludge spill that has now reached the Mississippi River.

A contactor's bulldozer slid into a pond earlier this week, leading to an hours-long rescue at the Hi-Crush mine in the western Wisconsin town of Whitehall. Rescuers emptied the pond to free the man, requiring them to release 10 million gallons (37.8 million liters) of water and mud into the Trempealeau River tributary.

The Wisconsin Department of Natural Resources is studying the sludge, but test results likely won't be back for a week. DNR spokesman Jim Dick said Thursday that Hi-Crush is cleaning up the area.

Meanwhile, the plume has reached the Mississippi River and Minnesota's pollution agency is monitoring it.