Marshfield Municipal Airport has received a $1.6 million federal grant to prepare the airport for a runway lengthening and widening project in 2013. Airport manager David Dinneen said the preparation work, scheduled to begin around Labor Day, includes tree and brush clearing at the approaches and creating new natural habitat for endangered species to mitigate the environmental impact of the construction. The grant covers the vast majority of the cost of this fall’s prep work; remaining funds will come from the state and the airport. The airport plans to add 300 feet of runway to meet the requirements of the Federal Aviation Administration, he said, and the expansion is expected to cost between $11 million and $12 million. The runway has never been rebuilt since its construction approximately 40 years ago, Dinneen said.