Here are some links that may help with research

Crystalline Silica Primer
Minnesota DNR-Silica
Minnesota Pollution Control-Silica Sand Mining
Republican Eagle article 11/26/14

Minnesota Pollution Control-Lake Pepin Sedimentation 
Minnesota Public Radio News-Lake Pepin Sedimentation  May 2011
Minnesota Center for Environmental Advocacy Lake Pepin sedimentation
Post Bulletin Article 4/10/14
Lake Scientist Article 1/6/2015