What level of accuracy is required for using GPS for wetland delineations?
The Philadelphia District requires a third order, class one level of accuracy for all wetland delineation surveys conducted by traditional plane surveying methods. This level of accuracy is assured by achieving an error of closure of 1 in 10,000. For wetland delineation surveys conducted using the Global Positioning System (GPS), the Philadelphia District requires that each wetland boundary point have a positional accuracy of +/- 15 cm (0.5 feet). In the event that vegetation or other obstructions prevent the effective use of GPS for surveying any particular jurisdictional boundary delineation, establishment of a separate baseline will be required. This baseline shall be tied to the respective state coordinate system, and each point of intersection (PI) shall be clearly marked on the ground. The jurisdictional boundary line shall be referenced to the baseline by station and perpendicular offset measured to the nearest 0.1 ft. When this occurs, the survey plan must indicate the location
