TransCanada's Gulf Coast pipeline project is closer to reality under a revised plan aimed at heading off ecological concerns. The U.S. Environmental Protection Agency and the U.S. Army Corps of Engineers took issue with several wetland crossings along the 480-mile route between Cushing, Okla., and Nederland, Texas, when they were proposed as part of the larger Keystone XL project last year. Instead of laying pipe over streams and wetlands, TransCanada now plans to go under them.
The oil company has worked closely with the Corps to address issues and expects the project will start construction this summer. "We continue to plan based on that [schedule]," says Shawn Howard, TransCanada spokesman. "We think we'll be able to meet that goal." The Corps would not reveal to ENR specific details of the proposed plan, but a source at the agency says the mitigation involves horizontal directional drilling (HDD).
HDD is a trenchless method often used in pipeline construction. A pilot hole is drilled first, using a guidance system to keep the drill on the right path. The hole is then widened through reaming; when complete, pipe can be pulled through.
The Gulf Coast project will use 36-in.-dia pipe, which would require a hole bored to at least 48 in. wide, says Samuel Ariaratnam, professor and program chairman of construction engineering at Arizona State University. The method is an ideal option for crossing under environmentally sensitive areas, he adds. Although the process can be more expensive, depending on geotechnical conditions, it also can be more efficient. "If you're going under a river, it's more economical and more sustainable," he says. "It's often faster, too, so you get better productivity."
TransCanada's Howard says the company isn't overly concerned about the cost. "We don't sit down and weigh solutions in terms of how much does it cost us," he says. "As a company, we sit back and say, 'What's the right solution here?' "
Still, engineers face an array of challenges, notes Greg Wilson, president of Sharewell HDD, a drilling company based in Spring, Texas. In many regions of the state, crews will have to drill through sand, which can collapse, and clays, which can swell. "Around the Houston area, clay is a big issue," he says. "It's a very sticky clay that likes to swell."
In swamp areas, crews need to find solid ground to stage heavy equipment. Areas also need to be set up for recycling drilling fluid. Generally, crews aim to drill more than 20 ft below the bottom of a swamp to prevent leaking those chemicals into the water, he says. "A lot of people prefer to drill in rock, if they can," Wilson says, noting that rock is a safer but much slower and more expensive option.
The HDD method is an attempt to stem environmental concerns. Following rejection of the Keystone XL project in January by President Obama, Trans-Canada withdrew its application for Keystone XL and moved ahead on the Gulf Coast phase, which would not require a presidential permit. In April, the company filed Nationwide Permit 12 verifications.
Addresses Previous Concerns
"At this point, it appears that there aren't any crossings that will have greater than a half-acre loss of waters," she said, noting the review process is ongoing.
The proposed route extends south from Cushing and then passes east of Dallas near Tyler, ending at refineries near Port Arthur. It also crosses through three Corps districts. The Corps' Galveston District has until June 25 to conclude its review, while the Tulsa District has until June 28. The Fort Worth District has requested more information from TransCanada, according to a Corps statement.
EPA is particularly concerned about impacts to swampland. In November, Jane Watson, associate director of EPA District 6's ecosystem protection division, wrote a letter to Galveston District representatives that drew attention to crossings of the Bald Cypress-Tupelo swamps. Dixon did not provide details about the crossings but said horizontal drilling would be used in those areas.
Ariaratnam notes that horizontal directional drills can cover more than 6,000 ft. Also, two drills can be used at either end of a crossing, intersecting in the middle for a total length of more than 12,000 ft. Engineers are planning a 14,000-ft intersecting bore under the Yangtze River, the longest ever attempted, he adds.
Vicki Dixon, regulatory program manager at the Army Corps of Engineers Southwestern Division, says the new permit application addresses previous concerns regarding 61 crossings that would result in greater than a half-acre loss. Loss of more than a half-acre is not allowed under Nationwide Permit 12, she explains.
