Posted on February 18, 2019
(U.S. Army Corps of Engineers File Photo)
Deepening of the inner Savannah harbor is getting closer to a start with testing of a required environmental mitigation project now underway.
The mitigation project includes testing of a dissolved oxygen injection system. The DO system is designed to replace oxygen in the river lost due to the deepening.
The Savannah Harbor Expansion Project, known as SHEP, will deepen the river from 42 to 47 feet to accommodate larger, fully loaded ships and allow for fewer tidal restrictions. The deepening portion of the project has two phases, the outer channel and inner harbor. Dredge work to deepen the the 20-mile entrance channel was completed in March of 2018.
The inner harbor deepening consists of 22 miles remaining in the harbor channel from near Jones Island to the Garden City port. Jones Island is between Fort Pulaski and Tybee Island.
Dredge work for the inner harbor phase, however, can’t begin until successful testing of a dissolved oxygen injection system is complete.
The DO system is at two sites, upriver near Plant McIntosh in Rincon and downriver at Hutchinson Island.
The system uses 12 Speece cones, four at Hutchinson and eight at Plant McIntosh. The cones are about 22 feet tall, installed. They are designed to dissolve pure oxygen into water extracted from the river, then push the water back into the river.
The U.S. Army Corps of Engineers report that the system can a inject a total of 40,000 pounds of oxygen per day into the river. SHEP is a project of the Corps.
With a deeper harbor, Corps officials have said, more salt water will enter the river and estuary, decreasing oxygen levels needed by not only fish, but the whole ecosystem.
“That sea water being more dense and at a greater depth drives oxygen out of the water that would normally be there. This oxygen injection system is to offset that incremental decrease of oxygen, Jason O’Kane, a former manager for SHEP, has previously said. A decrease in oxygen is also greater in hotter months.
As part of testing the DO system, on Thursday a dark pink dye was released into the Back River to assist with tracking the path of the oxygen injected water, said Corps spokesman Billy Birdwell.
Another dye release is planned for the Front River on Feb. 21.
“Recreational boaters in and around the Back and Front River areas shouldn’t be alarmed as the dye is not harmful to people, plants or fish,” Birdwell said.
New use of technology
The harbor deepening project has faced legal challenges from environmental groups and South Carolina government agencies, some of it focused on this unprecedented setting for Speece cones. The technology isn’t new, but it’s usually used in much smaller projects such as wastewater treatment ponds, rather than a 47-foot deep harbor with huge tidal swings.
A settlement reached in 2013 require the Corps to prove the oxygen system works as it should before inner harbor dredging can start. The agreement also allows the conservation groups and state agencies to restart their litigation over the project if they are not satisfied with the test results.
The testing is expected to be complete by mid-May.
Conservation groups would prefer to see the test take place in the summer when oxygen levels can get critically low, said Chris DeScherer, managing attorney for the Charleston office of the Southern Environmental Law Center.
“The river experiences problems in the warmer months so the best scenario is to gather data those months,” he said.
That doesn’t look like it’s going to happen. DeScherer expects to review the results of the testing in the fall during a 30-day comment period mandated by the settlement.
Reporter Mary Landers contributed to this report.
Source: savannahnow
