United states department of interior bureau of ocean energy management

1.5Borrow Areas

The South Pelto Borrow Area design is based on prior geophysical and geotechnical investigations in South Pelto Lease Blocks 13 and 14. Within the identified available borrow resource not utilized for Caminada Headland projects (BA-45 and BA-143), there are two (2) areas referred to as Expansion Area A and B, located on the southwest and northern borders of the BA-45 survey area, as shown on Figure 2-9. Area A is the larger of the two, and has a maximum length of 4,243 ft and maximum width of 3,478 ft. The surface area is approximately 190 acres. The sand thickness is up to 14 ft. Area B has a maximum length of 4,712 ft and maximum width of 807 ft, with a surface area is approximately 63 acres. The sand thickness is up to 18 ft. A 3-ft zone of allowable disturbance is included between the sand and the lower sediment horizons. The preliminary design cut volume is estimated to be 3.2 MCY and 1.5 MCY for Areas A and B, respectively. Preliminary Design cut volume estimates of suitable sediments within the South Pelto Borrow Areas A and B is approximately 4.7 MCY including a 1,000 ft offset from active and abandoned pipelines.

Material from this borrow area may be used for containment dike construction at East Timbalier Island, beach and dune construction at East Timbalier and West Belle Headland as well as the East Timbalier marsh platform construction.

Ship Shoal Borrow Area

The Ship Shoal Borrow Area is located in within the South Pelto Lease Blocks 12 and 13 on the east central portion of the Ship Shoal sand body on the Outer Continental Shelf (OCS). The Ship Shoal Borrow Area is located approximately 23 NM west-southwest of East Timbalier Island. Within the Ship Shoal Borrow Area, the seafloor elevations range from less than -27 ft to deeper than -34 ft NAVD88. The Ship Shoal Borrow Area is trapezoidal in form as shown on Figure 2-10. The dimensions vary with a maximum length of 9,600 ft and maximum width of 4,400 ft. The surface area is approximately 584 acres. The sand thickness is up to 17 ft. The average percent sand and grain size were computed to be 95% and 0.166 mm, respectively. A 3-ft zone of allowable disturbance is included between the sand and the lower sediment horizons. The Preliminary Design cut volume is estimated to be 6.5 MCY, including a 1,000 ft offset from active pipelines for Project construction.

Material from this borrow area may be used for containment dike construction at East Timbalier Island, beach and dune construction at East Timbalier and West Belle Headland as well as the East Timbalier marsh platform construction.

East Timbalier Marsh Borrow Area

The East Timbalier Marsh Borrow Area is located on the Little Pass Timbalier Ebb Tidal Delta approximately 9.1 NM west-southwest of East Timbalier Island, contiguous to the beach restoration borrow area utilized for the West Belle Pass Barrier Headland Project (TE-52). The East Timbalier Marsh Borrow Area is rectangular in form, as shown on Figure 2-11. The dimensions vary with a maximum length of 9,700 ft and maximum width of 2,300 ft. The surface area is approximately 441 acres. Water depths within the borrow area range from approximately 15 to 21 ft below NAVD88. The sediments ranged from silty sand varying in thickness between 2.1 to 6.6 feet overlying mixed sediments comprised of silt and clay. Subsamples of the surficial sediments had a mean grain size of 0.096 mm and averaged greater than 75% sand. The mixed sediments were generally described as very soft silty clay or clay with a high water content averaging greater than 50% which typically increased with depth. The Preliminary Design cut depth was set to -27 ft NAVD88 with a 3-ft limit of disturbance. The preliminary design cut volume is estimated to be 7.2 MCY.

Material from this borrow area may be used for the East Timbalier and West Belle Headland marsh platform construction.

West Belle Marsh Borrow Area

The West Belle Marsh Borrow Area is rectangular in form; however, it is separated into three subareas based on the previously excavation limits as shown on Figure 2-12. The West Belle Marsh Borrow area was previously analyzed for the West Belle Pass Barrier Headland Project (TE-52) and was estimated approximately 4 MCY of marsh material (silt and clay). The TE-52 Marsh Borrow Area was permitted and partially used to construction the TE-52 project but, was not completely exhausted in the construction of the project, leaving marsh borrow material available for cost-effective excavation. The West Belle Marsh Borrow Area is located approximately 2.5 NM south of the West Belle Headland. The overall dimensions have a maximum length of 3,050 ft and maximum width of 3,150 ft. The surface area is approximately 113 acres. The West Belle Marsh Borrow Area has marsh compatible sediment ranging in thickness from 10 to 20 feet. The Preliminary Design cut depths range from -31.0 feet to -50.0 feet NAVD88 along with a 3-foot limit of disturbance. The Preliminary Design cut volume is estimated to be 1.7 MCY.