By Daniel C. Brown

Hang onto your hardhat, we're going 900 feet deep into a salt mine. The day is bright with sunshine as five of us step aboard the elevatorlike metal box that will lower us to the upper level, 500 feet into the mine.

Because safety is of paramount concern in the mine, we're all fully equipped with safety gear: hardhats, reflective vests, respirators contained in little metal canisters, and hand lamps powered by heavy batteries hanging from our belts. The respirators will render harmful gases benign in case of fire. It's never happened in this mine on Avery Island, LA, but we're prepared for the first time it does.

All five of us grab hold of sturdy metal stirrups that hang from the elevator ceiling. The elevator begins descending, and as daylight disappears, all is silent and darkness envelops us. With a gentle bump on the bottom, we arrive at minus 500 feet.

Dim light from overhead fixtures reveals a cavernous salt mine as we step out of the elevator. The mine's "back," or roof, is more than 100 feet high, and the passageway is just about as wide. We climb into an aging open-topped Jeep, which springs to life with a throaty growl.

Welcome to the Avery Island salt mine, located 7 miles outside of New Iberia, in southern Louisiana. The mine is owned by Cargill Deicing Technology, which acquired it in 1997. As the Jeep lurches down the passage carrying us deeper into the mine, the headlights reveal rusty mining equipment abandoned years ago. We're told this is the oldest operating salt mine in North America; the current mine began operations in 1898.

In fact, Avery Island has been used as a salt source for several hundred years. Early settlers harvested the salt from natural brine springs on the island. During the American Civil War, the island's salt resources became a target for hostilities when the Union Army destroyed mining operations in 1863.

In just a few minutes, we reach our destination at 900 feet down. We find ourselves in a huge cavern more than 100 feet high and several hundred feet long, where a burly Model G780B Volvo motor grader is waiting to work. We're told it was disassembled into components, which were then lowered into the mine and reassembled. Cargill bought the grader less than a year ago, and we can't wait to see it spring into action to push salt.

But first a bit of geology is in order. Avery Island is actually a small hill, created in the deltaic wetlands by the upwelling of ancient salt deposits that exist beneath the Mississippi Delta. The salt was formed in a sea that existed when the supercontinent Pangea broke up some 200 million years ago.

Beneath the island, salt takes the form of a dome 1.5 miles wide and more than 5 miles deep. Geologists estimate that the dome contains 150 billion tons of salt. The current mine has six levels, and Cargill is actively producing salt on the two lowest levels.

The mine produces more than 10,000 tons of salt each day. The material is crushed and screened before being loaded onto barges or trucks for delivery to a variety of customers. Avery Island's salt is used in agricultural feed, in oil-field drilling muds, to deice pavements, to soften water, and to produce other chemicals.

At Avery Island, miners use the room-and-pillar method. Salt is excavated by blasting and loading out a series of rectangular entries and crosscuts. The blasting process leaves in place rectangular pillarsótypically up to half the original saltó—in a checkerboardlike pattern. Rooms are mined in a designed pattern by undercutting, drilling, and blasting. An undercutter cuts a horizontal slot, or kerf, along the floor of the advancing room to provide a relief for blasting. Next, a drilling rig drills a series of holes in the face, and a mixture of ammonium nitrate and fuel oil is pneumatically placed into the holes.

Blasting follows. It's always done at night with nobody in the mine, for safety's sake. A large wheel loader is used to load 64-ton trucks. Those trucks require haul roads and access roads between levelsóand that's where our Volvo motor grader becomes a vital player in mining operations.

"We were looking for a grader that was large enough," says Donald Pellerin, Cargill's superintendent of underground maintenance. "The one we had before was too small. We have 10 to 12 miles of roads to maintain, and we wanted a grader big enough to cover them all.

"We sized the grader by the moldboard. This one has a 14-foot moldboard and 243 horsepower at the flywheel. We compared it to another brand and found that the Volvo has plenty of horsepower for what we need. Plus, it's got a Tier II-compliant engine." He's referring to exhaust emission regulations set by the US Environmental Protection Agency.

"And we like the serviceability of the Volvo," continues Pellerin. "All the filters are readily accessible. And the operator comfort is good. We've put 260 hours on the grader, and it's been perfect. We've done no maintenance except routine preventive work, like changing the oil. We want it to last forever," he says with a smile.

Pellerin says that while some salt dust is always floating in the mine's air, the salt air is dry, so it doesn't corrode equipment any faster than normal. Salty air does mean, however, that Cargill specified an engine air precleaner for the Volvo. And, says Pellerin, "We change air filters frequently."

Miner Hoyt Fitch regularly operates the Volvo G780B. "I like it," he says of the grader. "It's comfortable, it's got plenty of power, and visibility is great." Maneuverability is very good, he says, and the controls are easy to operate.

"This grader should last us for 12 years," says Pellerin. "We get good support from our Volvo dealer, and we're counting on the machine to do a good job for years to come."

Daniel C. Brown owns TechniComm, an Illinois-based communications business.

GEC - July/August 2004