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Editor’s note: This article was updated Feb. 27 to include two additional signatories to the letter.

A group of 11 academic hydrologists from research universities around the Southeast wrote to the Georgia Environmental Protection Division Monday warning regulators that they’re using the wrong data to predict the effects of mining on the Okefenokee Swamp. The resulting analysis underestimates the risk of drought that mining brings, the hydrologists say.

After the letter was initially made public, two more hydrologists signed it.

Alabama-based Twin Pines Minerals is seeking permits from the state to mine for titanium dioxide near the Okefenokee National Wildlife Refuge. As part of the permitting process, the EPD issued a draft mining land use plan last month.

The plan outlines how Twin Pines will continuously remove more than 1 million gallons per day from a shallow aquifer to keep its mining pit dry. The company has also requested a permit to withdraw up to 1.44 million gallons per day from the Floridan Aquifer, which is deeper underground. In modeling the effects on the swamp of these withdrawals, EPD uses data from a river gauge at Mcclenny, Fla.

The hydrologists say that’s the wrong gauge to use and instead the model should use the Moniac gauge on the St. Marys River, located much closer to the swamp itself.

The strip mining targets an area called Trail Ridge, ancient sand dunes that form a natural dam along the eastern side of the Okefenokee. The hydrologists say the main question about the mine is the degree to which it will alter the movement of water in and out of the swamp.

Rhett Jackson outside the Suwanee River Eco-Lodge. Credit: Mary Landers/The Current

“(P)revious research has demonstrated very high correlations between flows at this (Moniac) gage and swamp water levels monitored by the USFWS,” they wrote. “The geographic position of this gage is ideal for analyzing potential effects to swamp hydrology of consumptive ground water withdrawals beneath Trail Ridge.

At 15 miles downstream, the Mcclenny gauge is too far away and much less connected to the swamp.

“Three-quarters of the area draining to this (Mcclenny) gage is in relative highlands of north central Florida,” they wrote. “The hydrologic inputs to this basin and the hydrologic behavior of this basin are in no way similar to that of the southeastern portion of the Okefenokee Swamp. Furthermore, the sheer size of the basin and its flows at this gage will mask the effects a fixed withdrawal would have where the river exits the swamp.”

The EPD previously indicated it chose the Mcclenny gauge because its data quality was higher.

A leading critic of that modeling, UGA hydrology professor C. Rhett Jackson, organized the hydrologists’ letter to EPD. Jackson has previously submitted memos to the EPD outlining his analysis, which indicates an increased risk of drought from the proposed mine.

“Using the Moniac gage, we see that the mine withdrawals are likely to cause a large and significant increase in the frequency and severity of drought in the swamp,” Jackson wrote in a Jan. 31 memo. “Conversely, using the Macclenny gage, we see nothing.”

Jackson sent the letter to 14 Southeastern hydrologists. One was traveling and could not meet the deadline of one week to respond. Three did not initially respond. But all those who did respond within the deadline agreed with his assessment, Jackson said.

Along with Jackson, the hydrologists who initially signed the letter are: Larry Band, University of Virginia; Stephen Schoenholtz, Kevin McGuire, and Daniel L. McLaughlin of Virginia Tech University; Diego Riveros-Iregui, University of North Carolina at Chapel Hill; Ryan Emanuel, Duke University; Matt Cohen, University of Florida; Courtney Siegert, Mississippi State University; Luke Pangle, Georgia State University; and Todd Rasmussen, University of Georgia. Jim Reichard of Georgia Southern University and Chris Anderson of Auburn University signed the letter after it was initially released.

EPD spokeswoman Sara Lips said Tuesday the division will not be responding to inquiries on technical questions until after staff has had a chance to evaluate all technical comments previously received and that will be received over the comment period.

“Good comments on the Mining Land Use Plan – additional analysis, data, technical perspectives, mitigation measures, etc. — helps EPD make better decisions and we look forward to the process,” she wrote in an email.  “EPD will prepare a public document responding to the comments made and indicating any changes to the proposal as a response to comments received.  Agency response to comments and finalization of the MLUP can take anywhere from several days to several months to complete, depending on the number and complexity of the comments received.”

Through a spokesman Twin Pines declined a request for comment.

EPD is accepting public comments on the plan through March 20, 2023.

The Tide brings news and observations from The Current’s staff.

Mary Landers is a reporter in Coastal Georgia focusing on the environment for The Current. It's a topic she covered for nearly 24 years at the Savannah Morning News, where she began and ended her time...