MICHIGAN CITY, Ind. (AP) _ The National Park Service is preparing an expedited process to seek proposals from contractors to try to determine what caused a section of dune to collapse at the Indiana Dunes National Lakeshore, burying a 6-year-old boy under 11 feet of sand.
 
  Ranger Bruce Rowe said Tuesday a contractor could start a conductivity study as early as next week to begin searching for possible anomalies in the 43-acre sand dune called Mount Baldy. Ground-penetrating radar will then be used to try to determine the exact cause.
 
  Rowe says the dune near Michigan City will remain closed for until park service officials are confident the area is safe following the July 12 collapse.
 
  Nathan Woessner of Sterling, Ill., was discharged Friday from rehabilitative care at a Chicago children's hospital.