MICHIGAN CITY, Ind. (AP) _ Work is scheduled to begin to try to determine what caused a section of dune to collapse last month at the Indiana Dunes National Lakeshore, burying a 6-year-old boy under 11 feet of sand for more than three hours.
 
  The National Park Service and the Environmental Protection Agency are bringing in ground-sensing equipment to begin searching for possible anomalies in the 43-acre sand dune called Mount Baldy.  The work is scheduled to begin Monday.
 
  That section of the park has been closed to the public since Nathan Woessner of Sterling, Ill., became trapped on July 12. Nathan was released last month from La Rabida Children's Hospital. Doctors said he underwent physical, occupational and speech therapy. He's scheduled to return for more rehabilitation.