Petersburg is on Mitkof Island in southeast Alaska, approximately 175 kilometers southeast of Juneau and approximately 1,050 kilometers southeast of Anchorage. The island is in the maritime climate zone and has mild winters and cool summers. Most residents on the island obtain drinking water from surface-water sources. Ground water may be an alternative drinking-water source. The Federal Aviation Administration owns or operates airway support facilities near Petersburg. They are considering environmental and hydrogeologic conditions when evaluating options for environmental compliance and remediation at these facilities. This report describes the climate, vegetation, geology, hydrology, and flooding potential of the area surrounding the Petersburg Federal Aviation Administration facility.