Third Addendum Phase I Archaeological Survey for the Proposed SR 25 Spur East at Mackay River Bridge Replacement, Glynn County, Georgia

The proposed project would consist of replacing the existing bridge on State Route (SR) 25 Spur East (County Road [CR] 582/Torras Causeway) over the Mackay River 4.8 kilometers (km) (3 miles [mi]) east of Brunswick, Georgia (Figure 1). The existing 792.8 meter (m) (2,601 foot [ft])-long by 22.9 m (75 ft)-wide bridge carries four lanes of traffic, two in each direction, with a 1.8 m (6 ft) inside flush median with concrete barrier, a 2.4 m (8 ft) outside shoulder along the westbound side, and a 1.8 m (6 ft) bike lane with a 1.2 m (4 ft) striped buffer between the travel lane and the bike lane on the eastbound side. The bridge was constructed in 1986 and was designed using criteria that are below current design standards. The superstructure of the bridge is also in poor condition with concrete deterioration and cracking. Areas of scour have also been noted around the concrete piers supporting the bridge. The existing bridge is classified as being in poor condition, therefore, replacement of the bridge is recommended.

The proposed bridge would be approximately 818.4 m (2,685 ft) long and 27.4 m (90 ft) wide. The bridge would consist of four 3.7 m (12 ft) travel lanes (two lanes in each direction) with 1.2 m (4 ft) inside shoulders with concrete barrier, 2.4 m (8 ft) outside shoulders along the eastbound and westbound sides with a barrier separated 3.1 m (10 ft) shared-use path along the eastbound side. The proposed bridge would be constructed on a parallel alignment approximately 61 m (200 ft) north of the existing alignment and the existing bridge would remain open to traffic during construction of the proposed bridge. The existing right-of-way (ROW) measures between 73.2 and 121.9 m (240 and 400 ft) in width while the proposed ROW is between 76.2 and 146.3 m (250 and 480 ft) in width.

Due to the proximity of fishing piers to the existing bridge, the proposed project would require the removal of the fishing piers in order to demolish the existing bridge and construct the proposed bridge. The fishing piers are remnants of the 1949-1950 causeway that carried SR 25 Spur East over the Mackay River, which was modified to serve as a public recreational facility during construction of the existing bridge in 1986. The fishing piers are historic and are a contributing feature to the National Register of Historic Places (NRHP)-eligible Brunswick-St. Simons Highway; however, they have not been maintained and have been closed to the public due to safety concerns associated with their deterioration. As part of the proposed project, the fishing pier on the west side of the Mackay River would be removed permanently; however, the Georgia Department of Transportation (GDOT) is currently exploring options for providing a replacement pier on the east side of the Mackay River, which is adjacent to a public parking lot and public boat ramp that provides access to the river.

The original Phase I archaeological survey for the proposed project was conducted by Edwards-Pitman, Inc. (EP) in 2018 (Kosalko 2018) and did not identify any archaeological resources. An addendum survey was conducted in 2019 to cover extensions to project limits (Kosalko 2019); this addendum survey did not identify any archaeological resources.

A revised ESB was established in August of 2020 that extended a minimum distance of 30.5 m (100 ft) beyond all existing or proposed ROW or easements, and also included a submerged (underwater) cultural resources survey, which extended 152.4 m (500 ft) north and south of the bridge centerline and was conducted by SEARCH, Inc. (SEARCH; Grinnan et al. 2021). Differences between the revised ESB and the prior survey areas resulted in the second addendum survey, which was conducted in September and October of 2020 (Kosalko 2021). During final design of the project plans, a portion of the current Area of Potential Effect (APE) at the western project terminus was found to extend 91.5 m (300 ft) beyond the limits of all prior surveys (Kosalko 2018, 2019, 2021).