CHARLESTON, S.C. — The long-awaited Charleston Harbor deepening project hit a benchmark Friday with the completion of all the field studies needed for the project.
Now the work of recent months will be analyzed and the U.S. Army Corps of Engineers will issue a draft environmental impact statement next year, Brian Williams, the project manager for the Corps, said Friday.
Maritime interests want the channel deepened from its current 45 feet to 50 feet to handle larger container ships that will call when the widened Panama Canal opens in 2015. The deepening project is now estimated to cost between $300 million and $350 million.
The final field studies were completed during the last two weeks when 49 core samples were taken from the bottom of the shipping channel as far as 15 miles offshore. The hardest material found was a consolidation of sand, shells and sediment.
“It’s classified as rock but it’s not exactly super-solid stuff,” Williams said. “There are a lot of little pieces of shell inside it. It’s loosely consolidated limestone and it looks more like what people would associate with coquina. It’s rock, but it doesn’t require dynamite to get it out.”
Had hard rock been found, the cost of the dredging likely would have increased. And the environmental impact statement would have to be more extensive because the effects of blasting activities on marine life would have to be considered.
The core samples will now be analyzed at a Corps of Engineers lab in Marietta, Ga.
A final recommendation on the deepening project from the Corps of Engineers is expected in 2015. Then it’s up to Congress to authorize the project and provide the federal share of the money.
Analyzing the bottom of the shipping channel has been done in several phases.
Last fall, researchers from Coastal Carolina University made passes over the channel using both sidescan sonar and a magnetometer. The sonar sends out a signal that, with the use of the computer, creates a profile of the bottom. The magnetometer records anything containing iron on the bottom.
Then, last spring, geologists working off a shrimp boat out of McClellanville, sent down wash probes to see where the consolidated material or rock begins beneath the shipping channel. In wash probes, water under pressure is sent down a pipe toward the channel bottom until it meets resistance.
The results of the wash probe study were then used to help determine where core samples of the channel bottom were needed.