Leatherman Terminal

The State Ports Authority plans to establish a saltwater wetlands mitigation bank across the Cooper River from the Leatherman Terminal (above) that's under construction at the former Navy Base in North Charleston. Provided/State Ports Authority

The presence of metals and pesticides in soil samples taken at a proposed saltwater wetlands mitigation bank on Daniel Island has the State Ports Authority spending more money on studies for the unique project.

The additional testing — to be conducted by the engineering firm Terracon at a cost of $350,233 — is part of the maritime agency's plan to convert its roughly 135-acre site for use by developers looking to offset wetlands they fill elsewhere. It would be only the second such site in South Carolina.

The new tests are necessary to make sure that sediment excavated and moved to recreate marshland and tributaries won't pose an environmental risk, according to Barbara Melvin, the SPA's chief operating officer.

To date, the authority has committed $890,224 to the project, which is across the Cooper River from the Leatherman Terminal that's under construction at the former Navy base in North Charleston.

The SPA, which operates the Port of Charleston, announced plans for the mitigation bank in 2017. It would join the state's only other saltwater wetlands bank in Beaufort County.

Developers would be able to buy credits in the bank to obtain permits for new roads or other projects that encroach on existing wetlands. The property eventually could be opened to the public for fishing, kayaking and other recreational uses.

There is no timeline for the  completion, and a formal permit application has not yet been filed.

"We were given a prospectus a while back and have been in ongoing discussions with them," said Sean McBride, spokesman for the Army Corps office in Charleston. "We're waiting on additional information from them."

Once the Army Corps and the S.C. Department of Health and Environmental Control give their approval, the authority plans to sell it to a group with experience administering mitigation banks.

The authority would use proceeds from the sale to pay for capital projects such as new equipment or construction of the new terminal.

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"This is one of the very few sites remaining where you can create saltwater credits, so we consider it valuable, and we look forward to discussions with others that consider it valuable," Melvin said.

The authority also might retain some credits to offset wetlands damage for some of its future projects such as a barge operation to move cargo from the Wando Welch Terminal in Mount Pleasant to the Leatherman Terminal.

If a permit is eventually issued, the authority plans to clear vegetation from the property and remove about a million cubic yards of dirt so tide will fill into the area twice a day. Spartina grass would then be planted to prevent erosion.

The mitigation bank site is adjacent to a 50-acre parcel to the north, which the SPA has leased to the S.C. Department of Parks, Recreation and Tourism for a public park. The authority also owns more than 1,000 acres south of the mitigation bank site where dredge material is disposed.

The mitigation bank property previously was a dredge disposal site and was used as a farm in the 1980s and 1990s, according to the Army Corps. It's part of the property where the authority once planned its Global Gateway container terminal — a project that was scrapped nearly 20 years ago because of public opposition.

Reach David Wren at 843-937-5550 or on Twitter at @David_Wren_