Posted: Saturday, June 9, 2012 --- 4:50p.m.

MADISON, Wis. (AP) -- The Wisconsin Department of Natural Resources is asking the state Department of Justice to prosecute two silica sand mining companies for pollution violations.

DNR spokesman Ed Culhane says they are the first two cases the agency has referred to the DOJ since the so-called frac sand mining boom started in the state.

The DNR alleges Preferred Sands of Minnesota failed to have a storm water pollution prevention plan in place when a dike embankment collapsed at a Trempealeau County mine. The March 3 collapse sent more than 2,100 feet of river mud into privately-owned land.

The Eau Claire Leader-Telegram (http://bit.ly/KTacW7) says the DNR is also recommending Interstate Energy Partners and Tiller Corp. be prosecuted for failing to maintain dikes and berms around a Burnett County mine where muddy water flowed into a creek entering the St. Croix River.

Copyright 2012. The Associated Press.