UGA professor explains mining process
Feb. 1—C. Rhett Jackson, University of Georgia professor of water resources, has expressed concerns about a proposed mining project near the Okefenokee National Wildlife Refuge, but he thinks he can do better.
He "presupposed" people would have a good understanding of how the mine planned by Twin Pines Minerals would work, which is why he is offering another explanation.
Mining supporters argue the effects of the mine would be analyzed downstream at the Macclenny gage where the basin area's average discharge is 4.4 times larger than the much closer Moniac gage where the river exits the swamp.
"They claim we should use the Macclenny gage because the data quality is better there," Jackson said. "That may be true, but the data are also irrelevant to the question at hand."
He said using the Macclenny gage is equivalent to analyzing a Mississippi River flooding problem in Minnesota by using data near St. Louis.
"Can you imagine what the residents of Minneapolis would say to this analysis?" he asked. "At the Moniac gage, the St. Marys is an intermittent stream. At the Macclenny gage, the St. Marys is a large perennial river."
Twin Pines plans to mine mineral sands from Trail Ridge by moving a 500-foot by 100-foot by 50-foot deep pit that will move back and forth across the ridge.
Groundwater seepage in the pit will be continuously pumped and evaporated using mechanical evaporators to keep the pit dry. Sands withdrawn from the ore beds will be processed similar to panning for gold, except machines will separate the sand by density.
"These mineral sands may comprise 5% to 10% of the ore beds but will be largely absent from the lighter sands above and below the ore beds," he said. "After the mineral sands are removed, the remaining sands will be returned to the pit, and the process just keeps moving."
There will be sand deficits after the processed sand is returned to evacuated areas, and the land surface will settle over time.
"The St. Marys River is classified as impaired due to several water quality conditions, including sediment, turbidity, and dissolved oxygen, all of which could be affected by discharges of mine process water," Jackson said.
That is why Twin Pines proposes to use mechanical evaporators, he said.
The mining project will also remove groundwater from the Floridan aquifer, increasing the frequency and severity of drought.
The estimated seepage during mining will average 1.128 million gallons a day. This estimate agrees with well equations calculated by other experts, he said.
"Surficial groundwater will keep flowing into the pit as long as it is pumped," he said. "The resulting water level in the pit will be lower than the Trail Ridge water table in all directions. Lowering the water table by approximately 50 feet at the point of the mining pit will bring the water level in the pit down to the same elevation as the typical swamp water level."
Half the water pumped from the mining pit will come from water that would otherwise flow into the Okefenokee swamp.
"This loss will be most noticeable during drought conditions, as it is this surficial seepage that helps the swamp during droughts," he said.
Drought conditions also increase the risk of wildfires.
"Increasing the frequency and severity of drought and fires will have effects on the competitive balance of plant species, resulting in a cascade of changes to plant succession that will alter the ecology of the swamp," he said.
Mineral sands mining on Trail Ridge will increase the possibility of drought in the eastern portion of the 438,000-acre swamp "with cascading effects on the ecosystem."
"It will increase the probability of wildfires on the swamp margin, which periodically cause major problems for the region, including large-scale loss of commercial timber, and it will increase the number of days on which recreational boating is not possible in parts of the swamp," Jackson said. "Furthermore, mining on Trail Ridge will damage the tourism potential of the Okefenokee Swamp to the detriment of the state and the region."
