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South Waccamaw Canal Dredging Horry and Georgetown Counties

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South Waccamaw Canal Dredging Horry and Georgetown Counties, South Carolina

The proposed work consists of hydraulic dredging in the South Waccamaw Canal. In detail, the project consists of removing approximately 60,000 cubic yards over approximately 8 acres. Once the dredged material is transferred through submerged pipes, mechanical dewatering will be accomplished through non simultaneous use of geotubes, mechanical belt press, or a similar method. Once the dewatered material is sufficiently dried, it will be transported to a final upland disposal site.

Specific Project Details Provided by the Applicant: The proposed maintenance dredging project includes approximately 2.2 miles of canal at an average bottom width of 30-feet. The proposed dredge depth is -5.0 feet Mean Low Water (MLW) with a 1-foot allowable overdepth for a total dredge depth of -6.0 feet MLW. The dredged area will extend from the face of the existing docks 30 feet into the channel. The proposed material will be dredged by a hydraulic cutterhead suction dredge. The proposed dredge material will be transported to the dewatering site via a temporary pipeline, which will extend under Highway 17 Business in the existing infrastructure used for the 2016-17 Murrell’s Inlet dredge project. The effluent water from the dewatering system will be discharged via a second pipeline (via the same infrastructure) into Parsonage Creek. The temporary pipelines will be laid along existing creeks and will have weights and anchors to ensure the pipeline stays in place and does not impact the nearby marsh grass or oyster reefs. Additionally, it will not require heavy equipment so no impacts to wetlands will occur. The pipelines will be removed after the completion of dredging. The pipeline will have weights and anchors to ensure the pipeline stays in place and does not impact the nearby marsh grass or oyster reefs. The pipeline will also have signs and buoys to mark its location and warn the boating public of its presence. Even though HDPE pipe floats, it immediately sinks to the bottom when dredged material is introduced during the dredging process. The pipeline will utilize Channel A in Murrells Inlet to access the dewatering site. The influent pipe will be submerged across Parsonage Creek and then move up the small slough adjacent to the SCDNR boat ramp, away from the Marshview Marina. The pipeline will traverse beneath Highway 17-Business via an existing 36-inch steel casing to access the dewatering site. The effluent pipeline from the dewatering site will utilize the same casing to return the water to Parsonage Creek between the SCDNR courtesy float and Marshview Marina. The applicant included two layouts for the dewatering site which represent possible scenarios/configurations for either geotubes or belt-presses Mechanical dewatering. Both dewatering operations will not occur at the same time. The successful dredging contractor will have a specific layout for the selected dewatering method. After the dredged material has sufficiently dewatered, it will be trucked to an approved, authorized disposal site.

Avoidance and Minimization: The applicant stated that the proposed dredging will be performed with a hydraulic cutterhead dredge with dredged material transported via pipeline. In addition, the applicant stated that impacts to marsh grass and oyster reefs will be avoided by a 10-foot minimum setback and visual observations of effluent water.

Proposed Mitigation: The applicant offered no compensatory mitigation for the proposed impacts and stated: No mitigation is being proposed for the project as no impacts to saltwater or freshwater vegetation will occur. The bid package for the maintenance dredging project will require that the contractor maintain a setback from existing marsh grass or oyster reefs, and that all pipeline routes will be outside vegetated wetlands. The pipeline will be weighted and anchored to avoid movement and potential impacts to any nearby vegetated wetlands.

Project Purpose: The project purpose as stated by the applicant is to provide year round boating access during all tidal cycles for private residencies on the creek and public access to the creek.

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