Lessons Learned

Allen Harbor Marsh Restoration, North Kingstown

Description | Construction | Elements of Success and Failure | Benefits

Allen Harbor Navy Davisville/Quonset Landfill in North Kingstown Courtesy: CRMC

Description of the Restoration
Allen Harbor is located on the west shore of Narragansett Bay in North Kingstown. The wetland restoration project took place in conjunction with the remediation of a U.S. Navy landfill that was used between 1946 and 1972 for the disposal of waste material generated by the Naval Construction Battalion Center Davisville and Naval Air Station Quonset Point. Reportedly, municipal type waste, including construction debris, rubble, preservatives, paint thinners, degreasers, Polychlorinated Biphenyls (PCB), asbestos, ash, sewerage sludge, 55-gallon drums, used mineral grit, and fuel oil were placed in the landfill. Foster Wheeler Environmental Corporation (FWEC) was the Navy’s contractor for the remediation of the landfill and restoration of the salt marsh.

The wetland restoration project at Allen Harbor was performed in December 1998 to compensate for wetland areas that were impacted or lost during the remedial construction activities associated with the Allen Harbor Landfill project. The areas that were impacted included coastal wetlands, tidal mud flats, and sub tidal habitats. The U. S. Fish and Wildlife Service (USFWS) and the Coastal Resources Management Council (CRMC) calculated the area of compensation to be 1.5 acres.

The wetland restoration project was designed by the USFWS and CRMC and consisted of replacing a 2-acre area of common reed (Phragmites australis) adjacent to Allen Harbor with salt marsh vegetation.

Construction
The construction of the project included removing all of the Phragmites in the area and lowering the elevation of the wetland to allow an increased volume of salt water to flood the area.

Landfill site after capping and stabilization with intertidal marsh grass at base of riprap Courtesy: CRMC

Excavation lines and grades were indicated by CRMC on topographic maps provided by the contractor. A survey was conducted of an existing stream that flows through the project area to control the location and elevation of the stream during construction. A floating silt curtain was installed at the discharge point of the stream to control the migration of sediments into Allen Harbor.

Phragmites and soil removal was performed using a low ground pressure bulldozer and a Manitowoc 4000W crane. The material was placed in an open field at Calf Pasture Point that was designated as a disposal site by the permitting authorities and the contractor.

Elements of Success and Failure
The wetland restoration occurred because the Navy’s contractor found additional contamination at the Allen Harbor landfill late in the project. Removing the contamination impacted delineated wetlands, tidal mud flats, and subtidal habitat, and it resulted in two acres of restored salt marsh consisting primarily of smooth cordgrass (Spartina alterniflora). Because the contractor was under time constraints and a disposal site was nearby, the entire restoration took only thirty days to complete.

Benefits of the Restoration
As can be seen here, a healthy stand of smooth cordgrass resulted from the restoration at Allen Harbor. The Navy, their contractor FWEC, CRMC, and USFWS were able to ensure that impacts to the habitats from the contamination removal were remediated and an existing impacted habitat was restored.

This site was created through a partnership of the: Coastal Resources Management Council Narragansett Bay Estuary Program Save The Bay®