Dissolved oxygen injection system a ‘remarkable success’

(From left) Bryan Robinson, a hydraulic engineer with Savannah District, Emily Johnson of Tetra Tech, and Hayley DiGiano with LG2 Environmental Solutions, conduct a test of SHEP’s Dissolved Oxygen Injection System, Feb. 21, 2019.

Last week we completed the report on tests for the Hutchinson Island dissolved oxygen injection system, an environmental mitigation feature of the Savannah Harbor Expansion Project (SHEP).

The report contains conclusive evidence demonstrating the downstream D.O. plant delivers results better than anticipated and exceeds the success criteria needed to proceed with deepening the inner harbor.

The tests sought to determine whether the D.O. plant could adequately mitigate for impacts to dissolved oxygen in the river anticipated from deepening the inner harbor channel. Success was measured in three areas:

1) Produce and deliver 12,000 pounds of oxygen per day into the river: We observed 13,385 lbs/day during the testing period.

2) Demonstrate at least 80% transfer efficiency of oxygen to the water: We observed an average of 95% or better transfer efficiency during the test period.

3) Adequate distribution of the injected dissolved oxygen in the river: We observed the dissolved oxygen mixes well in the water column and it remains detectable for days further up- and down-stream beyond what was expected.

In the words of our commander:

“The data-driven results of these tests point to an unmistakable conclusion: The dissolved oxygen system is a remarkable success,” said Col. Daniel Hibner, commander of the Savannah District. “The weight of evidence is immense.”

The 60-day test period involved collecting 24 million data points with an acceptance rate of 97.4%.

A back view of the Speece cones at the downriver Dissolved Oxygen Injection System on Hutchinson Island.

“From the very beginning, my team approached this challenge with incredible energy,” said Hibner. “We take our environmental stewardship very seriously. My team’s solutions-based approach and initiative demonstrate that the environmental component of the deepening is just as important to us as the navigation component.”

Tests ran from March 14 to May 12, which spanned two complete lunar cycles. The schedule was measured in lunar cycles to determine how the different tidal conditions during the testing period would affect distribution of super-oxygenated water in the river.

“Results documented in the report offer clear and verifiable evidence demonstrating an increase in oxygen during the days the system ran compared to the days when the system was shut down,” said Beth Williams, chief of the Hydraulics and Hydrology Section at Savannah District. “The difference in data with the system on versus off can be seen as clearly as flipping a light switch.”

Williams also emphasized the evidence collected using dye.

“The results from the dye testing showed that the water exiting the plant is rapidly mixed both vertically in the water column (top to bottom) and longitudinally in the river (well upstream and downstream from the plant) and that it stays in the system for several days following the event,” said Williams. “Dye tests helped us to better understand and visually see where the oxygen will go when it leaves the plant.”

The report and its appendices are posted here.

An aerial view of the Dissolved Oxygen Injection System plant on Hutchinson Island.

Injecting super-oxygenated water into the Savannah River helps mitigate for the loss of oxygen as the harbor is deepened from its current 42 feet to 47 feet. The SHEP will provide greater opportunity for modern container ships to enter and leave the port with greater loads and with fewer tidal restrictions.

The extra oxygen added to the river will benefit fish, particularly the endangered shortnose sturgeon and the Atlantic sturgeon as they pass through the area to upstream areas and back to the Atlantic Ocean.

The SHEP will benefit the American economy by a ratio of 7.3 to 1. That means for each $1 spent on deepening the harbor, the U.S. economy will see a net benefit of $7.30, or a net benefit of $282 million per year.

The Corps of Engineers uses Speece cones, giant steel cones which use river water, mixing at high pressure to dissolve pure oxygen into the water. The machinery then returns the super-oxygenated water to the river where tides and currents distribute it naturally.

Pure oxygen is extracted from the air at the Hutchinson Island location. As an automated plant, it requires little human involvement.

The system will be used mostly during the hot, summer months when oxygen levels in the river are naturally lower.

The successful demonstration of the dissolved oxygen injection system is a requirement before dredging of the inner harbor can begin. The outer harbor, from approximately Fort Pulaski to 19 miles into the Atlantic, was completed in March 2018.

The construction of a second dissolved oxygen injection system in Effingham County, Georgia, is almost complete. A second test is scheduled for the summer of 2020 with both upstream and downstream plants together. This second test must prove successful in order to continue with the deepening of the inner harbor.

~ Russell Wicke, Corporate Communications Office

About U.S. Army Corps of Engineers Savannah District

The U.S. Army Corps of Engineers Savannah District oversees a multimillion dollar military construction program at 11 Army and Air Force installations in Georgia and North Carolina. We also manage water resources across the Coastal Georgia region, including maintenance dredging of the Savannah and Brunswick harbors; operation of three hydroelectric dams and reservoirs along the upper Savannah River; and administration of an extensive stream and wetland permitting and mitigation program within the state of Georgia. Follow us on Twitter @SavannahCorps and on Facebook.com/SavannahCorps
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