MINNEAPOLIS — Wisconsin officials say early tests have found no harmful chemicals after a spill near a frack sand mine sent millions of gallons of sludge into waterways.

A contactor's bulldozer slid into a pond last month, leading to an hourslong rescue at the Hi-Crush mine in the western Wisconsin town of Whitehall. Rescuers emptied 10 million gallons (38 million liters) of water to reach the driver. The spill sent thick sludge into a Trempealeau River tributary, tinting waterways orange as the thick plume traveled downstream and into the Mississippi River.

The Wisconsin Department of Natural Resources has yet to release samples from metal and chemical tests Tuesday. Department spokesman Jim Dick tells the La Crosse Tribune that preliminary results show "no immediate toxicity."

Hi-Crush is cleaning up the area.