If you live anywhere near Augusta, you’ve probably seen the photo by now. On August 27, two local hunters, Mason Dodd and Tony Jones, pulled a 12-foot-6-inch, 570-pound alligator out of the Savannah River during Georgia’s season. South Carolina’s own public season opened at noon on September 12, so there’ll likely be a few more pictures like that before it’s over.
But some of the most studied alligators in the area live behind a federal fence. They’re downstream from Augusta, inside the Savannah River Site, in a lake the government built to cool plutonium reactors. And honestly, I think the dirt wall holding that lake in is even more interesting than the gators.
Par Pond was built to cool plutonium reactors
Par Pond is a 2,640-acre reservoir the government built in 1958 and 1959 by damming a creek called Lower Three Runs. The site made plutonium and tritium for nuclear weapons, and its reactors threw off an enormous amount of heat. Par Pond was basically a giant radiator. Hot water from the reactors went in, cooled off out in the lake, and got pumped back to do the job again.
It served two reactors, R and P, and that’s where the name comes from. According to a Los Alamos lab newsletter, “RAP Lake” was also on the table, but with Augusta and the Masters just up the road, Par apparently won. That’s a pretty good pun for a place the locals called the bomb plant.
R Reactor used the lake until it shut down in 1964, and P Reactor kept running through it until 1988. R also left something behind. Between 1954 and 1964, fuel or target slugs leaking in its storage basins let an estimated 222 curies of cesium-137 into the creek system, and the DOE’s 1992 analysis put most of it in the mud at the bottom of Par Pond and Lower Three Runs.
Mercury got in too, with the Savannah River water the site pumped in to keep the lake topped up. If the whole setup sounds familiar, we covered a Florida nuclear plant whose cooling canals turned into a crocodile nursery back in August.
Par Pond’s dam got a sinkhole in 1991
The dam’s an earth embankment about 65 feet high and 4,500 feet long. On March 14, 1991, a routine inspection turned up a dip on its downstream face roughly 3 to 4 feet wide and 1 to 2 feet deep.
So, a hole you could sit in.
It turned out to be a bigger deal than that. When engineers dug in, they found a column of soft fill running from the bottom of the dip down to nearly the top of the 8-foot concrete conduit that carries water through the dam. Crews filled and packed the hole, and a new, smaller one showed up in the same spot.
What worried the DOE was something engineers call piping. Water finds a path through an earth dam and starts carrying soil out with it, and the channel it cuts grows back toward the lake until there’s a straight shot through. The DOE also noted these pipes like to form right next to conduits, because the dirt packed around a pipe usually isn’t as tight as the rest of the dam.
The DOE couldn’t say for sure whether that was happening. Its special environmental analysis said the evidence pointed to a possible piping problem it couldn’t confirm or rule out, and it rated an immediate failure as unlikely. It lowered the lake anyway, mostly because of Martin, a small town 12 miles downstream.
So why didn’t they just patch the hole and leave the water where it was?
Because the water was the problem. The deeper the lake behind an earth dam, the harder it pushes, and the DOE wanted Par Pond down about 20 feet to ease that pressure and shrink the flood if the dam gave way anyway. Both reactors that had used the lake were already shut down, so there wasn’t anything on the site that needed it full. Frankly, when it’s a lake level against a town, that’s a pretty easy call.
Where did 16 billion gallons go?
The DOE started the drawdown on June 21, 1991. The site’s pumphouse sent water into other creeks through the old reactor supply lines, and crews ran siphons straight over the top of the dam, some of them 36 inches across. You can think of those as the world’s least relaxing drinking straws.
The big drawdown wrapped up on September 19, with the lake at about 182 feet above sea level instead of its usual 200. A Westinghouse Savannah River Company report that October came to about 16 billion gallons pulled out in roughly three months. A little over half went over the dam, and the rest went down three other creeks, all of which run to the Savannah River.
Here’s where it gets a bit weird. The same report put Par Pond’s full volume at about 17.4 billion gallons, and there were still around 5.5 billion left at the end. So how do you take nearly 16 billion gallons out of a lake that size and still have water in it? Rain. The report figures roughly 4 billion gallons of rain and runoff came back in while the siphons were running, which must’ve been pretty maddening for whoever was watching the gauges.
That left about 1,300 acres of lakebed out in the open air, the same mud the cesium had been settling into for decades. The DOE checked whether dust blowing off it could hurt workers and decided it wasn’t a significant risk.
A little of it reached the river
The Westinghouse report estimated about 160 curies of tritium and 0.21 curies of cesium-137 made it from Par Pond to the Savannah River, and it admitted the cesium number was on the high side. Curies tell you how much radioactive material you’ve got. Millirem tell you what it actually does to a person.
The report’s worst case was someone who’d drink the river water and eat a lot of its fish all summer, and that person came out at about 0.05 millirem, while the DOE puts natural background radiation around the site at about 300 millirem a year. I’d call that a rounding error.
Par Pond then sat low for about three and a half years. I couldn’t find a public document that spells out exactly which fix the DOE went with, though a 1994 engineering review looked at seepage, earthquake risk and adding a berm. Rain started refilling the lake in August 1994, the site began pumping in river water that December, and Par Pond was back to full pool by early 1995.
So are the alligators radioactive?
It’s the first thing everyone asks about these gators, and the people who study them say the answer these days is mostly no. Ben Parrott, then an assistant professor at UGA’s Savannah River Ecology Laboratory, told The Augusta Press in 2021 that radiocesium is still on the lab’s testing list, but “the levels are so low that they are not a major concern.” I’ll be honest, I couldn’t find a recent published cesium number for a Par Pond alligator, so I can’t give you one.
Mercury’s another matter. In a study published in January 2023, UGA researchers reported that harvest-size gators sampled in Par Pond averaged about 1.97 parts per million of mercury in their tail meat, against 0.64 for the ones in L Lake, the site’s other old cooling reservoir. The World Health Organization guideline the paper uses for food is 0.5.
The same paper says the 1991 drawdown stirred contaminated sediment back up and made more of Par Pond’s mercury available to wildlife. So by protecting a town, the DOE might’ve ended up putting more mercury into the lake’s gators. I’d argue that’s the most frustrating twist in this whole story.
The DOE did see some of this coming. Its 1992 analysis warned that adult gators might leave the shrinking lake, possibly off the site, and it included the line “Some of the alligators may be large and hence may pose a safety threat.” That might be the most government way anyone’s ever described a 12-foot reptile.
Those gators do get around. The UGA team caught two alligators in L Lake that had first been caught in Par Pond, about 4.8 miles away, and L Lake’s only about 5 miles from the Savannah River. The last headcount I could find for Par Pond itself is about 200 gators, and it’s from the late 1980s.
The researchers noted neither reservoir was open to alligator hunting, but they figured anyone eating gators that came off the site shouldn’t have more than one 3-ounce serving a month.
If you drew a tag for the Southern Coastal unit, which the UGA paper puts the site in, that’s advice written with you in mind. South Carolina’s public alligator season closes at noon on October 10.
