The National Environmental Policy Act (NEPA) Web site explains the requirement for environmental impact studies for federal agencies.
"Section 102 in Title I of the Act requires federal agencies to incorporate environmental considerations in their planning and decision-making through a systematic interdisciplinary approach. Specifically, all federal agencies are to prepare detailed statements assessing the environmental impact of and alternatives to major federal actions significantly affecting the environment. These statements are commonly referred to as Environmental Impact Statements (EIS) and Environmental Assessments (EA)."
Your state or county may have additional impact study requirements for non-federal agencies; contacting the state or county directly may be the best action: