Martin Marietta Materials Inc., a Raleigh-based supplier of building materials, is seeking to expand its operations in the Wilmington area, beginning with an expansion of its existing limestone quarry in Castle Hayne.

Founded in 1939, the firm operates more than 500 facilities across North America, including Canada and the Bahamas. In June, it announced a $13.5 billion deal to combine with Lhoist North America, a Belgium-based producer of lime and mineral-based solutions. 

This spring, Martin Marietta applied to expand its 1,422-acre limestone quarry in Castle Hayne, located in northern New Hanover County, to keep up with market demand. The quarry produces crushed limestone used as a sub-base material for roads, parking lots, construction fills for foundations and other large-scale projects.

"Our long-standing history and reputation at the Castle Hayne Quarry demonstrate our commitment to providing the region with a reliable, local source of crushed stone, aggregate, and construction materials while responsibly protecting the surrounding community and environment," wrote Thomas Brown, director of environmental and land services for Martin Marietta's east division, in an email to the Business Journal.

He added, "Martin Marietta takes its environmental stewardship very seriously and is working closely with the appropriate permitting agencies, stakeholders, and environmental experts to address any concerns about this project." 

The expansion would cover 732 acres, including 428 acres of wetlands and 14 acres of open water. The mining operation itself would grow by 358 acres. 

“Castle Hayne currently has limited available reserves to supply the growing market it serves in the medium to long term,” the application states. “Without augmentation, it will be unable to meet market demand in the long term.” 

The application also says that one of the major drivers of the expansion is the significant population and economic growth in the city of Wilmington and the surrounding Brunswick and Pender counties, “driving up the need for additional housing, infrastructure improvements, schools, shopping and office space.” 

Roger Shew, a local conservationist and geology and environmental science lecturer at the University of North Carolina Wilmington, said most of the wetlands included in the expansion are designated Waters of the United States, subject to federal regulation and protection. 

The application seeks a permit from the U.S. Army Corps of Engineers to permanently impact 143 acres of wetland and 9.7 acres of open water, with plans to avoid impacts to 284 acres of wetlands in the floodplain of both the Northeast Cape Fear River and Island Creek. 

In an email to the Business Journal, Shew added that the lowland areas along Island Creek will be most affected by a quarry expansion and deepening. 

“For mined areas, it will be extremely difficult, if not impossible, to restore a disturbed wetland area,” he said. “And even with mining directly adjacent to the floodplain, without adequate buffers, the lowering of the water table with mining…could negatively impact these wetland obligate species.”

Martin Marietta also filed an application with the N.C. Department of Environmental Quality (NC DEQ) Division of Water Resources for a Clean Water Act Individual Water Quality Certification, required to determine whether a proposed project minimizes impacts on surface waters or wetlands. 

According to the application, Martin Marietta would use stormwater management and erosion control techniques to preserve downstream water quality, including a minimum 50-foot wooded buffer between the mine site and the floodplain. Additionally, the company plans a minimum 500-foot undisturbed buffer along the Northeast Cape Fear River, according to Brown, as well as an average 500-foot undisturbed buffer along Island Creek. 

"In total, Martin Marietta proposes to place nearly 300 acres of the project's most environmentally sensitive wetlands in an undisturbed buffer," said Brown. 

Should the project be approved, the company proposes to purchase wetland mitigation credits at a 2:1 impact ratio, totaling 286 credits. 

Shew, in response, argues that a 2:1 ratio does not adequately mitigate loss or damage to a nationally significant floodplain. He adds that the compensation should be much higher, at 4:1. 

The application states there are no practical off-site alternatives and that the on-site expansion results in the least permanent impact to wetlands. Shew sees a feasible alternative: combining expansions at Rocky Point and at Castle Hayne’s upland areas, which he says could offer more than 50 years of mining. 

In addition to the Castle Hayne Quarry, Martin Marietta’s regional network includes Wilmington Sand, Leland Yard, Rocky Point Quarry and Onslow Quarry.

NC DEQ held a public hearing on the proposed expansion last week at the Heide Trask Senior High School in Rocky Point and is accepting written comments online or by mail through Aug. 13 at 5 p.m.

The division has 60 days from the end of the public comment period to make a decision about the expansion.