 Sanford Health and Marshfield Health System of Wisconsin have disclosed a plan to merge. Sanford, based in Sioux Falls, would be the parent company. Sanford Health President and CEO Bill Gasson would be the President and CEO of the combined system. Marshfield would have three seats on the Sanford Board of Directors. The deal is expected to be finalized within the next six months. Marshfield had been in negotiations earlier to merge with Duluth-based Essentia Health, but that proposal didn't materialize.