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HomeMy WebLinkAbout10153-AH-Narrative-0909191 Carteret County Navigation Project Atlantic Harbor Maintenance Dredging & Living Shoreline Permit Narrative Project Purpose, Need & Scope Carteret County (County) is requesting federal and state authorization to conduct maintenance dredging within the entrance channel and inner harbor of Atlantic Harbor of Refuge. The project will also construct a 1,735 linear foot (lf) granite rock sill supplemented by six (6) 25-lf engineered wave attenuators (total length 1,885 lf). The rock sill and wave attenuators will provide shoreline stabilization for White Point peninsula and marsh habitat restoration. A maximum of approximately 13,250 CY of material will dredged from Atlantic Harbor and placed on the White Point material placement area. Nominal size rock weighing between 350-lbs (18” diameter) and 900-lbs (24” diameter) will be placed to construct the 1,735 lf rock sill. An estimated 8,030 tons of granite rock will form the marsh sill with an additional 1,550 tons of Class A granite riprap used as bedding stone. Engineered wave attenuators will also be installed in 25-ft segments fronting breaks in the rock sill. The 15-ft breaks will enable fish passage and tidal flushing landward of the sill. The Atlantic Harbor of Refuge, authorized under Section 107 of the River and Harbor Act of 1960, was constructed in 1972. The harbor is in the unincorporated community of Atlantic in Carteret County and situated off Core Sound 3 miles west of Ophelia Inlet. Figure 1 shows the Atlantic Harbor vicinity in planview. The harbor is important to the local fishing industry as a place of safety, and access to the Atlantic Ocean. As such, the harbor facilitates a vital component contributing towards the continued longevity of the local community. Figure 1. Atlantic Harbor Vicinity Map (NTS) The Atlantic Harbor of Refuge is a federally-authorized project that has been historically maintained by the USACE; however, the USACE has experienced difficulty in dredging the harbor recently due to the lack of an upland material placement facility. The Wilmington District (SAW) notified Carteret County of the maintenance difficulties in June of 2017 and requested the County take actions to construct a placement facility and potentially dredge the harbor 1. Tab E (pertinent correspondence) provides the correspondence 1 Medlock, J. (2017, June 29) Letter to County Manager. USACE. Wilmington District. Atlantic Harbor CARTERET COUNTY, NC Sea Level Ophelia Inlet Beaufort Atlantic Ocean N Carteret County Navigation Project Atlantic Harbor Maintenance Dredging & Living Shoreline Permit Narrative 2 detailing the lack of a material placement area to receive the dredge spoil. In response to the USACE’s notification, Carteret County has secured a material placement facility and intends to maintenance dredge the inner harbor of refuge and entrance channel. The County will also construct a granite rock sill to provide shoreline stabilization and enhance marsh habitat restoration. The maintenance work will remove approximately 13,250 cubic yards (CY) of silty material from the proposed work areas as shown in Tab F (permit drawings). The maintenance work maintains consistency with the federal authorization for Atlantic Harbor and provides a maximum 40-ft channel at elevation -6-ft MLLW +1 through the harbor entrance. The template also generally maintains a 5H:1V sideslope to discourage additional sediment sloughing from the adjacent area. Within the harbor entrance, the side slopes increase to a 3H:1V to minimize the dredging footprint. The proposed channel width and depth also reduces within the harbor entrance to a minimum width of 16-ft at elevation -5-ft MLLW +1. Inside the harbor, the maintenance template maximizes the dredging potential by expanding to approximately 190-ft wide with 5H:1V side slopes. However, the template maintains the maximum dredge depth of -5-ft MLLW +1 as proposed for the entrance channel. Tab F (permit drawings) provides additional details describing the maintenance template. An emergency maintenance dredging project along the entrance of Atlantic Harbor was permitted (GP- 71340) and conducted in the summer of 2018 to provide short-term relief of the shoaling impacts. This maintenance dredging project removed approximately 1,000 cubic yards (CY) to create a narrow channel through a heavily shoaled area immediately outside of the harbor entrance. Tab G (Previous Permits) provides a copy of permit GP-71340 for reference. The County now intends to conduct a more extensive maintenance operation to provide a long-term solution for the local navigation needs. Additional maintenance projects have been conducted by the USACE since 1948. The original dredging of Atlantic Harbor removed and estimated 78,150 CY in 1945 and six (6) maintenance events since have removed over 98,270 CY. Table 1 shows the maintenance history of Atlantic Harbor between 1948 and 19682. Table 1. Maintenance Dredging History for Atlantic Harbor (1948 – 1968) Year Volume Removed (CY) 1948 10,058 1952 9,692 1959 51,249 1963 6,919 1965 Unknown 1968 20,354 TOTAL 98,272 Note: Table originally published in USACE, 1976. The USACE typically maintains the navigation channel for a width of 75 feet at elevation -7-ft MLLW with 3H:1V side slopes. Tab H (Atlantic Harbor Hydrographic Survey) shows the typical section maintained by the USACE for Atlantic Harbor along with an August 2018 hydrographic survey. The hydrographic survey shows elevations within the harbor entrance of -2 to -4 feet MLLW. Inside the harbor, elevations range between -4-ft and -6-ft MLLW. Therefore, the County is proposing maintenance dredging to restore navigational access and preserve the harbor of refuge status. 2 USACE, (1976). Final Environmental statement; Maintenance of the waterway connecting Pamlico Sound and Beaufort Harbor, North Carolina. Wilmington. Carteret County Navigation Project Atlantic Harbor Maintenance Dredging & Living Shoreline Permit Narrative 3 Sediment Compatibility To support development of a dredging plan and associated permitting, sediment cores from Atlantic Harbor were collected and tested in March 2018. Based on review of the analysis for geotechnical vibracore samples the dredge material is considered non-beach compatible and will be placed in an upland placement facility on nearby White Point. Tab I (Geotechnical Analysis) provides the geotechnical analysis of the dredge material. The USACE designated White Point as a material placement facility and protective breakwater for the harbor of refuge and entrance channel2. In addition to the geotechnical analysis, five sites were sampled for chemical analysis beginning inside the harbor entrance and extending southwest along the existing channel. Chemi cal analysis on the core composites was conducted in accordance with the USACE guidance, Sediment Testing Guidelines for Dredged Material Proposed for Disposal in Federal Project Disposal Areas by Applicants, along with other screening guidelines. Tab J (Chemical Analysis) provides the chemical analysis for the Atlantic Harbor samples. A risk assessment incorporated the chemical analysis results and showed some parameters exceeded selected screening levels. These included concentrations of certain metals, semi-volatile organic compounds, and pesticides within the harbor and near the entrance. Additional testing outside of the harbor showed decreased levels of these same contaminants. Semi volatile organic data for these stations were primarily non-detect or below the reporting limit and there were no exceedances of the screening levels. For metals outside the harbor, there were limited elevated concentrations (i.e., total chromium and manganese). Since there were some elevated concentrations of certain contaminants based on the screening results, further analysis of the cumulative effects of multiple contaminants entailed using a risk calculator developed by the Division of Waste Management (DWM). Designed to evaluate multiple exposure routes associated with contaminated environmental media, the calculator estimates the risks associated with current or potential future human exposure. The risk calculator incorporates the sediment core data from three sites representing the areas to be dredged that were selected in consultation with DWM staff 3. Application of the risk tool showed potential risk associated with arsenic and chromium for all three sites with the addition of thallium for one site. However, the cumulative risks under the User Defined receptor covering periodic use for a recreator and a trespasser on the island do not exceed the benchmark assumptions in the tool. Further, chemicals like arsenic, chromium, and thallium have natural and common anthropogenic sources that are likely influencing the results at these stations. The Resident receptor is not applicable in these cases because, the dredge disposal site, White Point, does not have residential development. In addition, Carteret County intends to file a deed stipulation disallowing any future residential development on the property. A copy of the recorded deed restriction shall be provided to DCM prior to the commencement of the dredging activities. In summary, the results demonstrate that disposal of the dredge material on White Point should not pose a significant risk to human health or water quality. Tab K (Risk Assessment) shows the risk calculations for the dredge material. Construction Methodology The project entails two (2) phases of work referenced as maintenance dredging and living shoreline. The maintenance dredging will be conducted first to minimize the potential for impacts to the living shoreline and to provide sufficient fill material to grade the marsh restoration area. An additional 300-CY will be 3 Robbins, S. (2018, October 4) Phone call to 910-796-7217. Carteret County Navigation Project Atlantic Harbor Maintenance Dredging & Living Shoreline Permit Narrative 4 necessary to fill the marsh restoration area above the excavation volume required to place the rock sill. Construction of the rock sill may begin prior to completion of the maintenance dredging, but an access way will be maintained for transporting the dredge material to the placement site. Maintenance Dredging Approximately 13,250-CY of dredge spoil will be directly placed in the White Point material placement area shown on Figure 2. Dredging operations will be conducted by a bucket dredge/excavator between November 16 and March 31 in efforts to minimize the potential for environmental impacts. Dredging activities will extend through day light hours but will not entail night time operations. Material will be dredged from the Atlantic Harbor channel and placed on a barge or other floating work plant. A turbidity control barrier will be utilized and remain until sediment in the water column has settled. The material will be transported to the disposal site on White Point. A backhoe or excavator will move the material from the barge to a truck or other hauling equipment on White Point where it will be placed and contained within an earthen berm. The ownership of White Point has not been determined and remains in question. Ownership could potentially fall to either the adjacent property owner, Carteret County, or the State of North Carolina. White Point formed from dredge material placement conducted with public funds, which suggest the site would be publically owned. However, White Point is attached to the adjacent property and therefore could also be considered as accreted lands. To resolve this issue, Carteret County has secured an easement from the adjacent property owner for construction and maintenance of the project. Tab L (White Point Use Easement) shows the easement letter provided as authorization to use the site. Figure 2. Material Disposal Site (White Point) The dredged material will be dewatered and placed within the upland disposal site with the intent of permanent storage. Earthen berms or silt screens will be used to prohibit the effluent waters from reentering the adjacent water bodies. In addition, turbidity curtains will be maintained surrounding the offloading site Atlantic Harbor White Point Carteret County Navigation Project Atlantic Harbor Maintenance Dredging & Living Shoreline Permit Narrative 5 during times of dredging activities. The curtains will be positioned to capture any sediment disposition spilling from the construction process. Prior to placement of dredge spoils, the spoil containment basin and berms /silt screens will be inspected to ensure the effectiveness and capacity to contain the material. The Division of Coastal Management (DCM) will be notified so a representative may inspect the site to help verify the appropriate BMPs have been established to help control the dredge effluent and material run-off. In addition, DCM will be notified immediately in the unlikely event of containment breech. Living Shoreline & Marsh Restoration Construction of the living shoreline and marsh restoration will entail placement of approximately 8,030 tons of 18-inch to 24-inch granite rock supported by approximately 1,550 tons of Class A riprap as bedding stone. Filter fabric will also be placed beneath the bedding stone to provide additional protection against settlement. The granite rock will function as a sill to tamper wave action and help stabilize the subtidal and supratidal habitat abutting the structure. Approximately 40,000-ft2 of subgrade will be shaped to establish a marsh planting area comprised of smooth cord grass (Spartina alterniflora) and saltwater cordgrass (Spartina patens) will be planted to help enhance the shoreline stability and habitat function. Additional vegetation suitable to the project conditions may also be planted as part of the restoration efforts. Placement of the granite rock sill and vegetation will occur outside of the dredge material placement area to reduce the potential for spreading or material run-off. The rock sill will generally be placed below MLLW. Along the interior of White Point, from station 0+00 to station 4+25 as shown in Tab F (permit drawings), the rock sill will be placed at elevation -1.5 MLLW with approximately 0.5-ft of bedding stone placed beneath. From approximately station 4+25 to station 17+35, granite rock weighing an average of 350-lbs (18-inch) will comprise the first 425-lf of the reef along the interior of White Point. Rock weighing an average of 900-lbs (24-inch) will comprise the remaining 1,310-lf. The 24-inch nominal diameter rock will be installed at elevation -2.5 MLLW and will also have 6-inches of bedding stone and filter cloth underneath to help prevent settlement. Fifteen (15) foot gaps will be spaced every 200 linear feet to allow flushing and fish passage landward of the sill. Large voids, created through use of non-varied rock sizes, will also allow fish passage and flushing throughout the sill structure. Approximately 3,000 CY of material will be excavated from within the proposed footprint of the sill to install the granite rock and filter cloth. This material will be redistributed immediately landward of the sill as backfill. The backfill will help create the marsh restoration area from approximately the MLLW elevation to +2 MLLW. An estimated additional 300 CY of dredge material will be needed to complete the grading and backfill proposed for the marsh restoration area. The marsh area will also be planted with approximately 75,200 spartina type plugs on approximate 9-inch center spacing. The marsh habitat and rock sill will provide stabilization to the White Point shoreline and enhance the habitat function. The granite rock will most likely be trucked to the site and placed by land based heavy equipment. Surveys will be used to verify the placement locations and quantities along with load tickets from the approved quarry. The attenuators will most likely also be constructed by land based equipment; however, water based installation may be implemented at the contractor’s discretion. Piles will be driven at approximate 4-ft centers to support concrete disks infused with shell. The disks will be installed over the piles to form a wave break. Tidal currents will be allowed and encouraged landward of the wave attenuator to promote flushing behind the rock sill. Carteret County Navigation Project Atlantic Harbor Maintenance Dredging & Living Shoreline Permit Narrative 6 Environmental Concerns Based on meetings with regulatory agencies in December 2017 and 2018, the anticipated major regulatory requirements include 408 Review through the USACE Civil Works branch, a Coastal Area Management Act (CAMA) major permit, and USACE General Permit (GP) 2878. The GP 2878 is issued by the USACE Wilmington District “to authorize maintenance dredging within federally authorized navigation channels and borrow areas, and the discharges of excavated and/or fill material within federally approved confined upland disposal areas or, in the case of beach quality sand, federally authorized beach retention areas or federally authorized beach nourishment project areas in the state of North Carolina.” Additional input from the resource agencies indicated no Biological Assessment for protected species nor a SAV survey would be required. However, as a supplemental resource for the permit review, Tab M (Atlantic Harbor Environmental Statement) provides the 1976 document evaluating maintenance dredging of Atlantic Harbor, along with other waterways connecting Pamlico Sound and Beaufort Harbor. The Wilmington District USACE authored the 1976 document. Also, as previously stated, dredging activities will be restricted to November 16 through March 31 for additional protection towards potential impacts. The cooler months generally offer a lower risk for environmental impact. Historic Resources An archaeological assessment has not been completed for the proposed dredging; however, the site is a federally authorized navigation channel and has been dredged since the 1940’s. North Carolina Environmental Policy Act (SEPA) The project involves expenditure of public funds and is in compliance with the North Carolina Environmental Policy Act (SEPA). SEPA applies for any project that meets all three of the following criteria, an environmental document must be prepared: 1. An expenditure of $10 million in funds provided by the state of North Carolina for a single project or action or related group of projects or action Or land-disturbing activity of equal to or greater than 10 acres of public lands resulting in substantial, permanent changes in the natural cover or topography of those lands (or waters) 2. An action by a state agency, and 3. Has a potential detrimental environmental effect upon natural resources, public health and safety, natural beauty, or historical or cultural elements, of the state's common inheritance. Since the project is less than $10 million and disturbs less than 10 acres of public land, further environmental documentation under SEPA is not required. Summary The County is requesting state and federal authorization to conduct maintenance dredging of Atlantic Harbor to aid navigation and preserve the health and safety of local boaters. A total of approximately 13,250-CY will be dredged and placed in the White Point material placement area, immediately adjacent to the harbor of refuge. The proposed maintenance dredging will restore the channel to depths in the inner Carteret County Navigation Project Atlantic Harbor Maintenance Dredging & Living Shoreline Permit Narrative 7 and outer harbor to -5-ft MLLW +1 to -6-ft MLLW +1 inclusive of a 1-ft overdredge tolerance. The County also proposes a granite rock sill to help protect and stabilize the White Point placement area. The rock sill will be supplemented by pile supported concrete disk wave attenuators to further prohibit wave propagation into the material placement area. Marsh restoration efforts will also be conducted landward of the rock sill to promote vegetation growth. The dredge material will be placed a minimum of 30-ft landward of the MHW line or landward of the marsh restoration area, whichever is more restrictive. Dredge material placement will not exceed 3.5-ft above the existing grade, or elevation +7.5 MLLW. Silt fencing shall be installed around the placement area, and shall be maintained for the duration of construction. Turbidity curtains shall also be installed around the dredge area to prevent the spreading of fines from the dredge sediment. Sediment analysis of the dredge material indicated the presence of some contaminants. However, consultation with DWM confirmed the material should not create a risk to nearby residents nor temporary visitors to the island. In order to further limit the potential for impacts from the dredge material, Carteret County will restrict residential development from occurring on the White Point Peninsula. Carteret County will provide this deed restriction as a pre-construction requirement for the maintenance operations. The granite rock sill proposed to surround the material placement area will limit the wave impacts and erosion to the White Point peninsula. The sill will provide breaks supplemented by wave attenuators to allow tidal flushing and fish passage. Marsh grass plantings will also be installed landward of the sill between MLLW and elevation +2.0 MLLW. The proposed work maintains consistency with the federally authorized channel for Atlantic Harbor, including the federal development set-back line established along the White Point shoreline. The proposed dredging remains within the authorized limits of the federal channel and the granite rock sill does not encroach upon the development set-back line. Carteret County intends to provide a long-term dredge material management site for the prolonged use of maintaining the Atlantic Harbor of Refuge and entrance channel. The County understands the environmental concerns associated with this project and has worked to provide minimization measures to allow a successful and complete project. These efforts include coordination efforts with state and federal resource agencies to identify potential concerns and also minimizing the construction window to the cooler winter months of November through March. The project also maintains consistency with the State Environmental Policy Act (SEPA). The overall project should provide a substantial benefit to the longevity of Atlantic Harbor and the surrounding community.